add datastore for exercice.
Merge branch 'master' of https://github.com/nicolasfavier/GAE-JS-AJAX
add api for exercices.
small stuff
Merge branch 'master' of https://github.com/nicolasfavier/GAE-JS-AJAX

Conflicts:
	war/WEB-INF/appengine-generated/datastore-indexes-auto.xml
	war/WEB-INF/appengine-generated/local_db.bin