simple teamcity support

Simple Teamcity integration for MergeRequest build status and link on a build.

Algorithm is very simple but it is working for us since 2014/07/15 and everybody happy :-)

Algorithm: get status of the last build in Teamcity for concrete Teamcity.BuildConfiguration_ID and MergeRequest.SourceBranch


Unused method argument - `sha`. If it's necessary, use `_` or `_sha` as an argument name to indicate that it won't be used. You can also write as `commit_status(*)` if you want the method to accept any arguments but don't care about them.<br>Unused method argument - `branch`. If it's necessary, use `_` or `_branch` as an argument name to indicate that it won't be used. You can also write as `commit_status(*)` if you want the method to accept any arguments but don't care about them.