Change callbacks don't always fire when adding a new child to a collection

[nwinter]

This is in 0.0.14. When I go from this:

... to this by adding the lol2 propert:

... no change callback is fired. If I edit the nested properties of lol2, it then says it's changed. I think it's the child add event that isn't triggering change.

[sderickson]

This was not a treema issue. The configSchema treemas were being passed in the raw data from the models, editing that raw data directly, and so messing up the model's internal attributes, breaking their revert system. Fixed in this commit: https://github.com/codecombat/codecombat/commit/3fd9cb89ef5cfdcc03364ce223ed644b8fd31229