MLECO-3164: Additional refactoring of KWS API

Part 1
* Add KwsClassifier
* KwsPostProcess can now be told to average results
* Averaging is handlded by KwsClassifier
* Current sliding window index is now an argument of DoPreProcess

Change-Id: I07626da595ad1cbd982e8366f0d1bb56d1040459
diff --git a/source/application/api/common/include/Classifier.hpp b/source/application/api/common/include/Classifier.hpp
index d641c22..e4eab01 100644
--- a/source/application/api/common/include/Classifier.hpp
+++ b/source/application/api/common/include/Classifier.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -34,6 +34,8 @@
         /** @brief Constructor. */
         Classifier() = default;
 
+        virtual ~Classifier() = default;
+
         /**
          * @brief       Gets the top N classification results from the
          *              output vector.
@@ -41,8 +43,8 @@
          * @param[out]  vecResults     A vector of classification results.
          *                             populated by this function.
          * @param[in]   labels         Labels vector to match classified classes.
-         * @param[in]   topNCount      Number of top classifications to pick. Default is 1.
-         * @param[in]   useSoftmax     Whether Softmax normalisation should be applied to output. Default is false.
+         * @param[in]   topNCount      Number of top classifications to pick.
+         * @param[in]   useSoftmax     Whether Softmax normalisation should be applied to output.
          * @return      true if successful, false otherwise.
          **/
 
@@ -65,7 +67,7 @@
             std::vector<ClassificationResult>& vecResults,
             const std::vector <std::string>& labels);
 
-    private:
+    protected:
         /**
          * @brief       Utility function that gets the top N classification results from the
          *              output vector.
diff --git a/source/application/api/common/include/Model.hpp b/source/application/api/common/include/Model.hpp
index 70c6245..4892757 100644
--- a/source/application/api/common/include/Model.hpp
+++ b/source/application/api/common/include/Model.hpp
@@ -137,13 +137,13 @@
         const tflite::Model* m_pModel{nullptr};            /* Tflite model pointer. */
         tflite::MicroInterpreter* m_pInterpreter{nullptr}; /* Tflite interpreter. */
         tflite::MicroAllocator* m_pAllocator{nullptr};     /* Tflite micro allocator. */
-        bool m_inited{false}; /* Indicates whether this object has been initialised. */
-        const uint8_t* m_modelAddr{nullptr}; /* Model address */
-        uint32_t m_modelSize{0};             /* Model size */
+        bool m_inited{false};                              /* Indicates whether this object has been initialised. */
+        const uint8_t* m_modelAddr{nullptr};               /* Model address */
+        uint32_t m_modelSize{0};                           /* Model size */
 
-        std::vector<TfLiteTensor*> m_input{};  /* Model's input tensor pointers. */
-        std::vector<TfLiteTensor*> m_output{}; /* Model's output tensor pointers. */
-        TfLiteType m_type{kTfLiteNoType};      /* Model's data type. */
+        std::vector<TfLiteTensor*> m_input{};              /* Model's input tensor pointers. */
+        std::vector<TfLiteTensor*> m_output{};             /* Model's output tensor pointers. */
+        TfLiteType m_type{kTfLiteNoType};                  /* Model's data type. */
     };
 
 } /* namespace app */
diff --git a/source/application/api/common/source/Classifier.cc b/source/application/api/common/source/Classifier.cc
index 6fabebe..1b5fc64 100644
--- a/source/application/api/common/source/Classifier.cc
+++ b/source/application/api/common/source/Classifier.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2022 Arm Limited. All rights reserved.
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -31,10 +31,9 @@
 namespace app {
 
     void Classifier::SetVectorResults(std::set<std::pair<float, uint32_t>>& topNSet,
-                          std::vector<ClassificationResult>& vecResults,
-                          const std::vector <std::string>& labels)
+            std::vector<ClassificationResult>& vecResults,
+            const std::vector <std::string>& labels)
     {
-
         /* Reset the iterator to the largest element - use reverse iterator. */
 
         auto topNIter = topNSet.rbegin();
@@ -46,11 +45,9 @@
     }
 
     bool Classifier::GetTopNResults(const std::vector<float>& tensor,
-                                    std::vector<ClassificationResult>& vecResults,
-                                    uint32_t topNCount,
-                                    const std::vector <std::string>& labels)
+            std::vector<ClassificationResult>& vecResults,
+            uint32_t topNCount, const std::vector <std::string>& labels)
     {
-
         std::set<std::pair<float , uint32_t>> sortedSet;
 
         /* NOTE: inputVec's size verification against labels should be
@@ -80,12 +77,9 @@
         return true;
     }
 
-    bool  Classifier::GetClassificationResults(
-        TfLiteTensor* outputTensor,
-        std::vector<ClassificationResult>& vecResults,
-        const std::vector <std::string>& labels,
-        uint32_t topNCount,
-        bool useSoftmax)
+    bool Classifier::GetClassificationResults(TfLiteTensor* outputTensor,
+            std::vector<ClassificationResult>& vecResults, const std::vector <std::string>& labels,
+            uint32_t topNCount, bool useSoftmax)
     {
         if (outputTensor == nullptr) {
             printf_err("Output vector is null pointer.\n");