pythonPackages: introduce sections, no functional change
pythonPackages: use unversioned to blend into pkgs, no functional change
pycairo: move to pythonPackages
pygobject: in pythonPackages, removed hack handled now by pth
fixup: pygobject rename pth
pygtk in pythonPackages, checks disabled, demo works, relates #223

Previously the checkPhase was not executed. It is now and a couple of
issues with it are seded away.