Mac: move qmacmime from cocoa to platformsupport

Prepare qmacmime to be shared between cocoa and ios.

Change-Id: If164b926b54240911a66f2a7f809d0066abab182
qmacmime: build/enable for iOS

Change-Id: I91bc5fae543a3ac5d4fbdb74793b1bf510ee05c0
qmacmime: enable mimetype uri-list for iOS

Just use the raw UTI directly (from Apple UTI reference) instead of
querying the system. Otherwise we would need to link to
MobileCoreServices.framework, which seems like an unnecessary
indirection.

Change-Id: I1f14cd1dd28cc3c35d91b72c2415f6e3b453778e
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