First save of POC
[poc] First work on chat page
Merge branch 'guimier-messages' into drogue-poc
[poc/languages] Finished merge
Merge commit '73f944f91ab4a4bc59624177077fef5ef16d8d2f' into drogue-poc
1st commit of drogue-design, inspired by drogue-poc + guimier-connexion

Relative design of page-chat
Update of page-login (center box)
Addition of disconnect button and hello to user.
Merge remote-tracking branch 'origin/drogue-design' into teyssier-fichiers
An abstract class Entity for User and Channel created.