Several improvements (#9)

* fix icon filename

* update pp2d to fix preview problem

* several improvements:
- rely on a single header for simple/common headers
- cleaned up main by putting the interface drawing function in its own file
- load previews from .zip themes (may cause some loading times when launching
- only need 1 shuffle image thanks to pp2d's blending abilities

* not needed anymore

* fix preview color and position

* forgot

* add proper icon loading
thanks steveice10 for bannertool which this was pretty much taken from

* only add proper themes to the list

* add slightly more space between the icon and the name

* not monospace, the little movement every blink is annoying

* fix typo

include/unicode.h

@@ -27,7 +27,7 @@
 #ifndef UNICODE_H
 #define UNICODE_H
 
-#include <3ds.h>
+#include "common.h"
 
 ssize_t strulen(u16*, ssize_t);
 void struacat(u16 *input, const char *addition);