try to get qtwebkit working on Windows
update release script for dealing with multiple qt5 submodules
improvements to handle chroot builds more easily
add chroot environment for performing MinGW-w64 builds

This is required as the MinGW-w64 environment for Ubuntu 14.10 is
broken. Rather than trying to fix it, it makes sense to use a known
good environment (i.e. Ubuntu 14.04) for performing the builds.
port the MinGW-w64 target