Cocoa: QMenu refactor.

Cocoa: QMenu refactor.

This change prepares for enabling native menus
on OS X.

Move code from src/widgets to cocoa:
- qcocoaapplicaiton
- qcocoaapplicaitondelegate
- qcocoamenuloader
- qcocoamenu
- qmenu_mac
- misc helpers to qcocoahelpers

Create a QNSApplication and
QCocoaApplicationDelegate at application startup.

New Lighthouse API:
- class QPlatformMenu
- class QPlatformMenuBar
- QPlatformIntegration::createPlatformMenu()
- QPlatformIntegration::createPlatformMenuBar()

Platforms that wants a native menu integration
subclasses QPlatformMenu[|Bar] and implements the
create function. The default implementation returns
0, which causes QMenu to use the standard Qt
menus.

This API is based on the current native menu
abstraction that Mac, Wince and S60 uses in Qt 4.
The main difference is that the platform classes are
proper standalone classes and not #ifdeffed into
QMenuPrivate.

Change-Id: I3da41f80b0ae903a476937908b1f9b88014b7954
Reviewed-on: http://codereview.qt.nokia.com/4068
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>