Rewrite the Mac native toolbar classes.

Rename the classes to QMacToolBar and QMacToolBarItem.
(Keep the Qt-style ToolBar name capitalization.)

API-review and document a core set of the API, remove
the rest. Missing functionality can be added back
later on.

Add a simple QWindow-based mactoolbar example that
shows the core toolbar functionality. Add manual
test for more comprehensive testing.

Make the QToolbarItem properties actually work,
you can now change the text and icon after the
toolbar has been displayed.

Update license headers.

Change-Id: I99fb207df7f1b3cf0d5df178aa863c77cd372a1f
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>