Cocoa: QImage -> CGImage conversion cleanup

Move to one qt_mac_toCGImage function that has simple
semantics and properly retains a copy of the QImage
for the lifetime of the CGImage.

Remove the old qt_mac_toCGImage function which had
two problems:

1) It would not retain the QImage data (this was probably
ok for its original use case: creating short-lived
CGImages for the paint engine)

2) It had acquired a somewhat odd **datacopy out
parameter for the cases where you _do_ want to retain
the image data.

This makes the exported image conversion function
from QtMacExtras work: The CGImages it creates will
no longer reference free'd memory once the QImage
is deleted.

Change-Id: I583040d16aefb17fc3d801d6b047a0b2a76c7f74
Cocoa: create QCocoaMimeTypes for Cocoa-only mime-types

Prepare to move qmacmime out of the cocoa port and into
QPlatformSupport for sharing with iOS. This patch will
start by moving tiff out, since it depends too much on
old carbon image manipulation code that will not compile
on iOS (depends on ApplicationServices etc).

Conflicts:
	src/plugins/platforms/cocoa/qmacmime.mm
Cocoa: move qmacmime to platformsupport

Move qmacmime to platformsupport so it can be shared between
cocoa and ios.

Change-Id: If164b926b54240911a66f2a7f809d0066abab182
qmacmime: bugfix unicode::canConvert

The UnicodeText convertor is a bit special since it can convert
to both utf8 and utf16 for text/plain. But since flavorFor("text/plain")
can only return one UTI, it returns utf16. And this means that
canConvert will return false if given the utf8 as argument.
On iOS this is often the only format available on the pasteboard, which
means that pasting text from another app into a Qt app will fail.

This patch will fix the text so that it returns true for both utf8 and
utf16.

Change-Id: Iac3fd8cd235fbad4e27c707c0d56a3c3d12848ee
iOS: implement clipboard

Change-Id: I0df17ff6fa8fc8c23615f2c016fae667e1f1d56b