Provide Qt modules as CocoaPods pods

Would be nice to be able to add Qt as a dependency to an Xcode (for any of the 4 Apple platforms) project using CocoaPods.

The idea is to follow the create_prl, create_pc, and create_cmake features of qmake, generating podspecs for each module in $QT_INSTALL/lib/podspec 

Hopefully there's a way to then ask cocoapods to use these local podspecs without too much trouble.

The alternative of publishing podspecs to the official podspec repository, pointing to our binary download packages, would mean that we would have to maintain these podspecs, making updates for each version, etc.

The preferred solution with local podspecs would allow using cocoapods with a locally installed Qt, either built yourself or via the Qt installer, or even via homebrew.