Make FindPyKDE4 work with PyQt's new build system.

Since PyQt 4.10, PyQt.pyqtconfig is deprecated and not available unless
PyQt is built using the old configure script.

PyKDE4 itself has recently been adjusted to mimic PyQt itself and only
install its pykdeconfig module if pyqtconfig is present. Additionally,
information such as SIP flags and the directory where PyKDE's SIP files
are installed are now also provided in the
PyKDE4.kdecore.PYKDE_CONFIGURATION dict.

This commit completely rewrites FindPyKDE4.py to make it look like
FindPyQt.cmake after commit a7e47438: most of the information used by
FindPyKDE4.cmake is fetched from PyKDE4.kdecore, and we first try to
obtain the SIP flags and directory from pykdeconfig and, if it fails, we
use PYKDE_CONFIGURATION.

Furthermore, FindPyKDE4.py now only prints the variables that are
actually consumed by FindPyKDE4.cmake -- it is not possible to obtain
all the data provided by pykdeconfig in PYKDE_CONFIGURATION. We've also
stopped reading and setting PYKDE4_VERSION_TAG, since PyKDE4 stopped
setting a KDE tag in 2008 (and its value was 3_92_0 at the time).

CCBUG:  327633
REVIEW: 119454