Converted to Gradle

This is a big change obviously, and also kind of a preference thing, so I won't be *too* upset if you turn this down, but I like it, and I hope you will too.

I'm not a big fan of maven build systems, mostly for their xml buildscripts and the size they can be. I love gradle for its way of making things simpler, and for making it easier for someone to just clone and build without too many prerequisites (eg, the gradle wrapper vs. installing maven prior). This implements Gradle as the build system. Just clone and run `(./)?gradlew(.bat)? build`, and it should make the .exe, .zip (with the .app inside), and the .jar files in the `build/distributions` directory.

Now for some notes. You need to install launch4j and have it in your PATH for this to work. This is very annoying to me, and I actually found maven's way of this better, as the launch4j maven plugin just downloaded the workspace for you and launch4j itself. (I feel like writing a better launch4j plugin now :P). Also, it seems weird to add the `Class-Path` when you're just shadowing your deps anyway, so I've commented out the adding of that (also because it was acting derpy :P).

Nothing else that I can think of off the top of my head. Let me know your thoughts.

EDIT: Forgot to mention that it also makes setting up a workspace for your IDE much easier as well. (`(./)?gradlew(.bat)? (eclipse|idea)`)