Add mod management files: mod_manager, mod_manager_ui, dependency_tree
Should be working, but the window isn't showing properly. not sure why not o.o
Need to add in the input interaction stuff to the UI, and the ability to load the mods
UI now working again! huzzah for that! Now to get mods loading, which means shoving all of the core files into a core mod and rejiggering when stuff actually gets initialized so that it is not immediately on application start!