Start pulsating ("breathing") the dot when app is launched

Start pulsating ("breathing", fade in, fade out, fade in, fade out,...) the dot when as soon as an app is launched by clicking on the icon in the Dock.

Some apps take many seconds until they show a window on the screen. During this time, the Dock should show that the computer is working.

Stop pulsating and make the dot solid color once app loading is complete (as it is now).

cc @reionwong