System tray initial support
Added initial support for system tray icon. This will be disabled by default (for now), to enable this feature set variable SystemTray to True in configuration file ~/.fbmessenger/config.py . For now system tray just has two options for right click to hide/show application and to quit it. Left clicking system tray will hide/show application. For now closing the main window will quit application instead of minimize it to tray (to see if it   will be better to minimize it).
System tray initial support
Added some file that are related to previous commit.
Update README to describe System Tray setting
tray-on-close

If the SystemTray flag is set the messanger now minimises itself to tray
on close.

It is done by additional argument _closable in BrowserWindow
constructor and additional object TRAY_EVENT in it.

Windows marked _closable=True are closed imidiately. Windows marked
_closable=False are minimised to tray (Main window only).
Merge pull request #1 from letalvoj/tray-on-close

tray-on-close
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
Enable System Tray by default. Removed a traling whitespace.
Updated comment for SystemTray configuration variable
Enable System Tray by default. Commented SystemTray and MinimizedOnStart parameters from configuration file. Update README.
Add capability to memorize if the app was minimized to tray or not when was closed and to start minimized or not according to this. MinimizedOnStart option can be used to enforce minimized startup.
Format code
Fix a bug regarding chat window still popping up when application is launched, even if the chat window was closed before closing the application.
remove trailing whitespace
make closable a keyword-only parameter
`is_system_tray_enabled()`

Create a wrapper for fetching the "SystemTray" setting, so that we don't
have to keep repeating the name and the default value, and so that we
can check `QtGui.QSystemTrayIcon.isSystemTrayAvailable()` at the same
time.