Multigraph support for gletters

Gletters now supports multigraphs as well.

For the languages where the alphabet had been translated, I moved the information over to the new level XML files. Localizers should still adjust the level design though, because I don't know which letters are hard to type on the keyboard layouts people are using.

I'll write up something on the Wiki, do you want me to send something to the mailing list once I'm done?