Add branchName as argument to specify what branch to build in TeamCity.

[KiyoIchikawa]

Newer versions of TeamCity support branchName as an argument in the API call to initiate a build: https://www.jetbrains.com/help/teamcity/rest/start-and-cancel-builds.html#Start+Custom+Build

[KiyoIchikawa]

I was having issues uploading a test build of my plugin to XLRelease to test, so I only submitted the actual code changes. I resolved the issues I was having with uploading the test version and validated my changes work as expected. I'll be submitting another PR to update all the gradle build information to work with newer versions of XLRelease.

[KiyoIchikawa]

Also just noticed that I did not update the readme to indicate the new optional argument for TeamCity.Build. Will have that update pushed later today.

[KiyoIchikawa]

Readme updated to include new arg passed to TeamCity.

[KiyoIchikawa]

Build updates here: #24