[Mac] MacPlatform doesn't need static ctor
[Mac] BXC10404 - Xamarin Studio cannot be closed from the dock when it doesn't have focus

Conflicts:
	main/src/addins/MacPlatform/MacInterop/GtkQuartz.cs
	main/src/addins/MacPlatform/MacPlatform.cs
Added PlatformService.IsModalDialogRunning()

Mac platform can now provide a more reliable implementation
that takes native dialogs into account.

Conflicts:
	main/src/addins/MacPlatform/MacMenu/MDLinkMenuItem.cs
	main/src/addins/MacPlatform/MacMenu/MDMenuItem.cs
	main/src/addins/MacPlatform/MacPlatform.cs
	main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.Desktop/PlatformService.cs
	main/src/core/MonoDevelop.Ide/MonoDevelop.Ide/DesktopService.cs
Added missing using System.Linq statement