Clean up Tomboy's code

Clean up Tomboy's code

This removes the unused tomboyutil code, as well as using a GTK+ function
to get the accelerator names. This reduces our code size quite a lot.

Code size reduction: (for a stripped, non-debug build)
before:            43468 bytes
remove tomboyutil: 43372 bytes
remove egg-code:   39256 bytes

So we save a total of 4212 bytes. Pretty good.