Support PyQt installations without pyqtconfig.py.

PyQt's pyqtconfig was deprecated in version 4.10, and is not installed
if PyQt's new build system is used.

PyKDE itself provides a pykdeconfig module that inherits from pyqtconfig
and allows users of the SIP build system to obtain information about how
PyKDE was configured and generate Makefiles from it. It is also used by
kdelibs's FindPyKDE4.cmake for the same purposes.

Even though the information provided by PyKDE exists regardless of
pyqtconfig, insisting on pykdeconfig goes against the design of PyQt's
new build system.

Instead, we now do something similar to PyQt itself: while it provides a
PYQT_CONFIGURATION dict with (at the moment) a single key with the SIP
flags used to build PyQt, we provide PyKDE4.kdecore.PYKDE_CONFIGURATION,
a dict containing the SIP flags used to build PyKDE and, in addition to
that, the directory where PyKDE's SIP files have been installed. This
new dict exists regardless of how PyQt was built.

Finally, this commit does ...