Add 'Disconnect' menu item to MUCs
Currently, if MUC has 'Minimize on close' flag raised, MUC is minimizing to roster when close is clicked.
But if user wishes to swiftly disconnect from some particular MUC, he need to turn off 'Minimize on close' before closing or first click close in MUC and then find this MUC in roster, click RMB and click disconnect.
Maybe it will be much faster to user, if MUC would have 'Disconnect' option in it's popup menu.