ZKL: fix for issue #84 and 2 other

multiple tweaks

Changes:
1) TextWindow.cs stabilize scrollbar during spam
2) fix typo in "ADDUSER" safety counter
3) fix issue #84 , middle-mouse-button now actually ask Server to leave a room
4) fix issue #85, having PrivateMessaging with same name as Channel now won't broke the Channel tab. 5) HistoryManager write chat-lines to file in delayed/buffered/burst style (related to no.4)
6) Advertiser, Multiplayer & Rapid UI TAB do "lazy UI initialization" (only initialize when opened. Aiming for efficiency). 

ops I miss this message.

Not sure what is the advantage over "_chan" to tab's internal name, or is it big advantage enough to do so.