[Mac] add cursor support
[Mac] add CursorType.Move

swap hand cursors:
* CursorType.Help -> NSCursor.OpenHandCursor
* CursorType.Move -> NSCursor.ClosedHandCursor
Merge branch 'add-mac-cursor-support' of https://github.com/sevoku/xwt into sevoku-add-mac-cursor-support

Conflicts:
	Xwt.Mac/Xwt.Mac/ViewBackend.cs
Merge branch 'sevoku-add-mac-cursor-support'