ZKL aesthetic tweak: attempt to minimize white margin at edge of ZKL MainWindow
HeadlessTabControl.cs: additional tweak to minimize white margin
MainWindow.cs: Tooltip now can appear for 3 window at once, previously only 2 (work as long as windows not overlapping too much).

Strip out colour char from system tray popup message (because there's no way to colour it there & it might make ZKL look unpolished)
ToolTipHandler: listen to a Control's dispose event & trim the Tooltip list rather than just adding new tooltip without limit.
ToolTabs.cs: fix https://github.com/ZeroK-RTS/Zero-K-Infrastructure/issues/222 & also make Tooltip appear on Linux for the Chat channel list.

"MouseOver" event doesn't seem to be called for the ToolStrip button, must use "MouseEnter" and/or "MouseLeave".
BattleBar.cs: fix https://github.com/ZeroK-RTS/Zero-K-Infrastructure/issues/217 by saying "New report arrive at zkadmin channel" and point at chat/zkadmin when receiving Rang from Nightwatch (if receiving Rang from somebody else, will use default message pointing at chat/Battles)
HeadlessTab & Navigation Control: make Nav buttons & the Content window to have clean precise fit (no chat window appearing under Back or Forward button)
BattleBar.cs: add a comment
Merge pull request #223 from xponen/zkl_whitemarginedge_reduce

ZKL: ui tweak & fix, tiny improvement in look