buildenv/1.3.x/win32-static: use Qt 5 instead of Qt 4.
buildenv/1.3.x/win32-static: update prep.cmd to point to Qt 5 instead of Qt 4.
tools: update fixup-prl-files.py to work with Qt 5.
buildscripts/1.3.x: update mumble-win32-static.cmd and mumble-win64-static.cmd for Qt 5.