Teamcity integration using 8.1 rest api

This allows gitlab to get build status from teamcity and to trigger builds on push

known issues
*cant read build Que
*triggering builds will only work for teamcity 8.1+

I am aware of the existing pull request #8434 

teamcity configuration
the teamcity server will need to have a user added for gitlab.
 the projects build configuration will need to use the git hash for the build number so that the build can be located from the api.
server for merge requests to build server must be configured to build all branches