TeamCity meta runner

Happy to submit this to https://github.com/JetBrains/meta-runner-power-pack if you think that's a more appropriate place. I just figure it's easier for you guys to keep it up to date in this repository?

I have successfully run this on a TeamCity server.

There are three things to note:

1. You can't include spaces in the `execArgs` or `projArgs`
2. Once this gets a gitversion installed on the server from Chocolatey it will never try and update it - I could include a call to `cinst` to update it if necessary every run, but that will add at least 1-2s (if not more) to every build run due to Chocolatey's slowness. That's why I'm checking the filesystem for chocolatey rather than invoking a Chocolatey command to see if it already exists.
3. While it will fail the build if there is a problem, it won't fail the step (the PowerShell script always returns a 0 exit code unfortunately) so any steps after it that are marked as "Run if all previous steps successful" rather than "Run if build successful" will still run