Implement Github Oauth

[bryanwong8]

Is your feature request related to a problem? Please describe.
Transfer Github Oauth logic and User models from bit-backend repo.

Describe the solution you'd like
Implement Github Oauth for users

Routes/functions to implement/change

• /login - to let users signup/login with Github GET
• /logout- to let users logout GET

Additional context
The routes should be in their respective Flask-Restful classes.