Make App Modular using proper classes

[betterclever]

App can be made modular using Proper Classes for objects like notes .
Currently JSON is being parsed by field, Gson ( https://github.com/google/gson) should rather be used to get object directly from JSON using proper classes

[betterclever]

@anonymous-ME This would be required for retrofit, I guess I should do this too for that. Or I'll be making model classes, you may later add GSON support in code.

[anonymous-ME]

@betterclever I will add GSON support in code later.