Case insensitive for model label

[sveetch]

Is your feature request related to a problem? Please describe.

Currently inclusion and exclusion definitions are case sensitive on model label: auth.user won't work, auth.User is valid.

Describe the solution you'd like

This may be simpler to have case insensitive. I don't think there is added value to keep case sensitive.

It has been developed with case sensitive because it was not clear if case mismatching could happen with between models from applications, however Django itself in dumpdata manage case insensitive so it seems we could stand on this.

This means we probably have to lowercase everything from appstore. This change should be retro compatible with definitions written with case sensitive.