Add support for sign-in / sign-up using JFBConnect

[manojLondhe]

• Need a new resource in the existing users plugin - jfbconnect so that it can be accessed at /api/users/jfbconnect
• The Resource accepts 2 parameters -

- provider (google/facebook) 
- access_token (the token provided by the login step in the app)

• The resource will receive these inputs and invoke the JFB Connect code to fetch / store a Joomla user based on their access token.
• Once the user is identified, the resource will create a user object for that user and set in the response. The object needs to have

 - id (user id) 
 - auth (API token old format) 
 - jwt (JWT API Token) 
 - name 
 - username 
 - email

If the access token and/or provider is invalid the resource will return an appropriate error