Repo cleanup: Improved the .gitignore and removed unecessary files from repo

This pull request cleans up the repository a bit by removing a bunch of unnecessary files. All the Visual Studio/Monodevelop files aren't really needed since Unity will create those when needed. It's usually a best practice to ignore them. 

I also improved the .gitignore by adding a bunch of ignores for the files that don't need to be tracked, and adding a few more useful ones.