Added missing silence.aiff file
Made the app stay in the status bar instead of the Dock
Added a way to restore the system icon, and added a confirmation popup on hide

 * The icon can be restored by relaunching the application from the Finder
 * On application launch, the icon will be hidden if it was hidden before
Added Launch on Startup option in tray menu
Removed useless keyboard shortcut in tray menu
Merge pull request #1 from alexandreblin/master

Moved from Dock to system status bar and added launch on startup