Improve chat behavior on disconnect

[valerio]

Currently when you disconnect or get disconnected the chat windows become completely grayed out (and unusable).

KMess should be able to discriminate between

• voluntary user disconnections (exit or login from another locations)
• server-side disconnections (errors or timeouts)

Then:

If the user quits/disconnects, all chat windows should be closed.
If the user gets disconnected, the windows should gray out, but only the input fields & emoticon sidebars.
If then the user reconnects with the same account, they should be enabled again; but if the user connects with another account, they should remain grayed out.

[valerio]

Fixed some weeks ago.