[WIP] Add verified access_token parameter authentication.

Allow access_token authorization. This time secured and verified by `/debug_token` Facebook API call (APP_ID and scopes are compared).

## TODO
- [ ] ensure this is right way (please confirm)
  - @asmatameem #167
  - @felipekk #167 
  - @damianorenfer #160 
  -  @fredkelly #90
- [ ] handle case when token is expired (it raises app_id doesn't match error)
- [ ] raise custom error when scopes are not met
- [ ] add tests
- [ ] refactor code