Merging Avalanche engine

This pull request is about the Avalanche engine, which is used to run Avalot d' Argent.
Most of it is implemented and the game itself is completable.
You can find the list of the missing parts on the wiki page of the engine in an order of importance under the name of 'TODO': http://wiki.scummvm.org/index.php/Avalanche 
My plan is to implement these missing modules even after the end of this year's GSoC. (That's why I am brave enough to open this pull request.)
The game has been freed by its authors and will be soon available on ScummVM's FTP server for the voluntary testers. You can also find a walkthrough for the game on the wiki which could help: http://wiki.scummvm.org/index.php/Lord_Avalot_d%27Argent/Walkthrough
If you have any observations, please don't hold it back!