- clarified that Qt Mac Extras is also applied to iOS.
- edited name of Mac App Store.
- changed instances of "Mac" or "Mac OS X" into "OS X".

Change-Id: Ic5a93fc1e25f239bf7cc5ff493f2108627d219b3
Task-number: QTBUG-40759
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>