New fixes in the current APIs implementation

[Himan10]

• Remove write access of specific fields present in each model, helps from Mass assignment.
• Re-write or introduce more better approach to update_application/ API implementation logic.
• Introduce json token verification on server-side
• Discuss for new changes in the Moderator APIs
• Add more APIs and functionalities to the existing APIs
• Rewrite file upload functionality

[Himan10]

@Parth858