[#8267] Add granted_at field to UserToken.
[#8267] Make UserToken.expiration_date nullable.
[#8267] Don't set user token expiration date by default.
[#8267] Wildcard fresh user tokens.
[close #8267] Fix get_access_token.
[close #8267] Exclude old tokens without expiration date.
Merge pull request #21 from Kern3l/master

#8267 Expiration date in Facebook tokens