Max Gunner: Level Editor

Added a couple of features to the Level Editor. You can now test the music track you've selected for your level in the properties panel. I also added a couple of different "draw" modes: the original single-block mode, a click-and-hold rectangle feature, and a click-and-hold hollow rectangle feature. Both of the click-and-hold methods work for added blocks and removing them. I am still testing everything, but thought you'd like to see the progress. Once they're tested, I will upload the new version. Enjoy!

-Spencer