add json_request decorator with test-cases

[nitinbhojwani]

This PR includes:

1. decorator json_request to parse input from request and keep it in request.data
2. test cases for newly added decorator

Behaviour of json_request:
By default, assume_json = True and request.data = {}

     1. If assume_json is True,
            > parse request.body as JSON; if error occurs in parsing, skip.

     2. If assme_json is False,
            > If request's method is GET parse request.GET for data
            > Else If request's method is POST parse request.POST for data

[nitinbhojwani]

@jsocol : Please do a review.

[nitinbhojwani]

Please review this PR.