* add smart response checks for ref discovery
Added content-type check and content regex check for reference discovery
see https://github.com/schacon/igithub/blob/master/http-protocol.txt
* move ref check constants to TRANSPORT class
the check constants - content regex and responce Content-Type - don't have to be global right now so moved from zif_abapgit_definitionsto zcl_abapgit_git_transport
* PP and activate