MenuStyle: Add pressed property to style data object

[ChangeLog][Styling] Add pressed 'property' for MenuItem styling
in styleData object

Task-number: QTBUG-40178
Change-Id: Id5c2af529ed67981415fb055ce83e2c528da525a
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
OS X: fix positioning of non-native menu popups

Change-Id: Iafc7f3a1a41093628e3cba8dd2a7781c2b82b021
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
MenuStyle: fix separator height

Let the delegate choose separator height instead of forcing a height
calculated based on the font size, and check styleData.type instead of
styleData.isSeparator that doesn't exist.

Change-Id: Ia395a27ea86087f772606a252adf7565868ceac9
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>