Feature moderation

See merge request chehabfl/outgoing_rex!13

Need to clean it and to add test for when moderation is not activated.

Squashing history by user added
Closes #11

Cleaning and Optimizations, more to go

App renamed from rex to backend to be clearer

See merge request chehabfl/outgoing_rex!12

Most backend models created, will need testing and tweaks !

See merge request chehabfl/outgoing_rex!11

All modules should be close to ready