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.
lang activity: added an enter the text exercise.

The image is displayed and the text is shown with the first
letter, dots and the last letter. The children must enter the text
and press enter.
lang activity: improved instructions
minor, now the intro voice is played when help is clicked.

Before that there was no way to hear again the intro voice.
Fixed typo in string
Updated Spanish translation
Updated POTFILES.in
Updated Greek translation
Updated Slovenian translation
Uniform gettext for config title

- translator controls order of paceholders
- individual contexts to avoid potential grammar problems with paceholders
Uniform config header, so it will only have to be translated once. Can't define context in Python yet
Added a comment.
Uniform gettext. Did't plan to commit this yet, because the file is out of date, but can't merge upstream otherwise
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/gletters-activity/gletters.c
	src/gletters-activity/resources/gletters/Makefile.am
	src/gletters-activity/resources/gletters/default-gd.xml
	src/gletters-activity/resources/gletters/upper-gd.xml