[FIX] im_chat : change the conversation header style to avoid overflow
[IMP] im_chat : remove a useless cr.commit(), but keep the other one to avoid TransactionRollbackError when conversing without many tabs opened
[FIX] im : remove the preventDefault (js) to avoid popup on reload page
[FIX] im_chat : TransactionRollbackError by allowing write user presence only if TIMEOUT is over, and fix the disconenction detection and notification