fixed possible scope validation error for password, client_credentials and extension grants while retrieving access token

FriendsOfSymfony/FOSOAuthServerBundle#190
Merge pull request #40 from FriendsOfSymfony/hotfix/grants-scope-validation-fix

Fixed possible scope validation error...
Current implementation retrieves bearer access token from entity-body only if its POST request. Bearer token usage spec states that other HTTP methods are suitable too.

FriendsOfSymfony/FOSOAuthServerBundle#94
Merge pull request #41 from FriendsOfSymfony/hotfix/bearer-token-authorization

fixed bearer access token retrieval