Added StyleCop Support

with some rules we seem to disagree disabled. This is not really based upon https://github.com/OpenRA/OpenRA/wiki/Coding-Standard but more or less what @pchote does and @chrisf mourns about at the moment. Maybe we can clarify the conventions here.

There is a [StyleCop](https://stylecop.codeplex.com/) AddIn for MonoDevelop that displays warnings when you right-click and ask for it. I tested this against it. Note: there is a problem with inheritance `..\` vs `../` which breaks a solution wide settings file so I had to copy & paste the file into each projects directory. :/

Even though I disarmed it, we have >1000 warnings per project. Once we agreed on standards and those get fixed, we could have our CI check for those automatically in the future so we don't have to manually tell everyone how to format the code with each new contributor pull request. Also helps me write code in accordance if I have some lint tool to warn me when I am doing it wrong.