* Handle magic cart properly.

This commit adds code to properly handle magic carts.

It also adds some configuration options not added in the sample config file in previous commits.

As well I forgot to do a makemigrations on my previous commit. This is necessary because we added new type of services like XMPP. The DB still works perfectly without this migration applied (tested both in sandbox and my test environment) because at the end of the day the service field for Limit and ExternalBundle is just an int... but is better to include the new migration for completeness.