`is_system_tray_enabled()`
`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.

oconnor663/fbmessenger,oconnor663/fbmessenger,oconnor663/fbmessenger