Invite listener receives request id on complete

Invite listener onComplete method has an extra param for request id
generated by facebook. This id is needed to be stored by the client app
in most cases
Delete request added

deleteRequest method to enable deletion of facebook requests by client.
See
https://developers.facebook.com/docs/android/app-link-requests/#step3
for details of the need.
Getting apprequests added

Added me/apprequests that retrieves a JSONArray of pending requests. One
can list them in client side or just delete them as needed.
Added postScore for Scores API

In games, scores can be posted using this function.
Also added code documentation for deleteRequest.
Merge pull request #39 from koraybalci/master

Invite listener receives request id on complete