Add a connection command queue

[valerio]

When performing too many actions in a too small time frame, the server reports being 'flooded' and won't accept more commands for a limited amount of time.

MsnConnection and/or the sockets need to cope with this possibility queueing all commands to send, and then by only sending a maximum number of messages per ~10/15 seconds (not sure about the time frame), keeping the others in queue for later.

When reaching a certain maximum, KMess should also warn the user that he/she's doing too many actions.

A possible side benefit of this may be that, if you try sending multiple requests for the same action (i.e. request a chat or change personal message), KMess could detect this and only actually send the last queued one.