tray-on-close - clean

Cleaned the tray on close fix. It is cleaner for the window to be
set closable according to the SystemTray setting instead of a wild
if/else conditions in browser.py...
minimize-on-start

Additional option MinimizedOnStart was introduced. This option is only
valid if the SystemTray option is True.
Typo in README.md
Typo in README.md #2
fixed "chat window closes main window" bug

Renamed TRAY_EVENT to HIDE_EVENT. Chat window is not closable=False and
listens for HIDE_EVENT to hide itself. This prevents the bug when
minimised main window was killed while closing chat window.
Merge pull request #2 from letalvoj/tray-on-close

Additional MinimizedOnStart option and fix a close chat window bug