Refresh token removed in Client Credentials Grant

As defined in RFC: http://tools.ietf.org/html/rfc6749#section-4.4.3
Fixed broken unit test. Fixes #28
Method to get all headers for the error response

Method added to get all required headers for the error response, according to the RFC - the correct HTTP status code and the "WWW-Authenticate" header in special cases.
Variable name fixes + little changes to support unit tests
getExceptionHttpHeaders() unit tests
Merge branch 'feature/http-headers' into develop. Fixes #29
Added grant to getClient calls. Fixes #21
getScopes() now have the grant type and client ID passed
Move authorisation code grant stuff into own grant
Added getResponseTypes() method
Added stateParamRequired method
Removed die(var_dump())
Merge of upstream corrections into develop branch