lang-activity, normalize the number of triplets to 12.
lang-activity: new activity with a large word dataset

Review a set of words. Each word is shown with a voice a text and an image.
When done you are suggested an exercice in which, given the voice,
you must find the right word.

The images and voices comes from the Art4Apps project: http://www.art4apps.org/
Based in the hard organisation work of Lionel Laské in
his online version accessible at http://laske.fr/abecedarium/
Multigraph support for gletters

- letters are now defined in XML for flexible level design
- moved the data over from the po files where alphabet had been localized, but localizers should still fine-tune

- bugs that still need fixing:
--- mode switching to mixed/uppercase -> load new wordlist!
--- uppercase_only: second element of digraph has to be typed uppercase
--- check hash compare again
Finalized multigraph support for gletters. Fixed bugs:

- mode switching to mixed/uppercase now loads new wordlist and resets sublevel
- interrupting a level and moving to a new one now resets sublevel
- uppercase_only: second element of digraph can now be types upper- or lowercase
- hashtable to avoid duplicate letters now works
gletters: improved fallback if uppercase wordlist not found:

first try to load default for the locale, then if that fails, try to load english.
gletters: added support for french including accents.