Fixed Crash while trying to login from facebook

Fixes #343 (closed)

Changes :
As the crash was mainly due to the fact that the user data was not getting saved in the local db, so first I changed the return type of the api in the retrofit interface to "AuthResponse" because the api response was different than that of the data class and then I simplly saved it in the local db.

Video for the change :
screen-20210327-114241

Appetize Link :
https://appetize.io/app/jkhn57ejunr06ypj2phpdca1m0?device=pixel4xl&scale=75&orientation=portrait&osVersion=10.0