In ordering_sentences (not the other two ordering activities), when updating datasets within the activity, I get the following error:
qrc:/gcompris/src/activities/ordering_numbers/ordering.js:35: TypeError: Cannot call method 'split' of undefined

This is due to the fact that the items.levels are updated in line 43.

There are two points to fix:

• This object should not be updated (I'll make a commit on all the activities to mark them readonly)
• We should be able to switch between datasets.