Allow users to input unicode escape sequences in the edit glyphs text area

I did this because I would rather type out the escape codes than do whatever hand contortion required to type the unicode characters in on Linux. 

The escape codes go to a single code point after "ok" is pressed on the dialog.
The escape codes are case insensitive.

I'm not sure how to build the standalone FontPackGUI.jar, so I'll leave that for you to rebuild.