Organized Headers, Modern Logos and Objective-C Support, Previous Track Bug Fix

General organization of headers to fit a less complicated pattern, and compile without warnings (removes need for ```GO_EASY_ON_ME```). Modified to fit modern Logos and Objective-C styles, including ```.xm`` [pre-processed file usage](http://iphonedevwiki.net/index.php/Logos#Extension_for_Logos) and NSInteger/CGFloat substition. Adopting NSInteger, in particular, fixed the recurring bug where the ```-prevTrack``` method continuously produced unexpected results.

You can [grab a build](https://github.com/insanj/MusicGestures/releases/tag/1.4.1) of this fork if you'd like to test it yourself!