Rewrite model frontend to be json-driven.

Change-Id: Iac786eff96183938d2fd11cde9313c6e8e1270a5
diff --git a/.gitmodules b/.gitmodules
index c112866..e06268d 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -4,3 +4,6 @@
 [submodule "thirdparty/serialization_lib"]
 	path = thirdparty/serialization_lib
 	url = https://review.mlplatform.org/tosa/serialization_lib
+[submodule "thirdparty/json"]
+	path = thirdparty/json
+	url = https://github.com/nlohmann/json.git