Rewrite MC gradle build files

This does unfortunately mean that someone is going to have to learn gradle (a fate worse than death), but we can't just leave it in the half broken state that it's in; with missing features and random/unknown pieces of useless tutorial script. Issues may exist with the script that we don't even know about. Finished script should be simple (but complete), clean, and fast (should check if a build actually needs to be done).