Drop dependency to libplasma from kwineffects library

Since the EffectFrames have been moved into KWin core nothing in the
Effects lib actually used Plasma. The only remaining method is moved
to core as it's not used in the Effects. The Effects itself still
link against Plasma, so nothing changes for them.

The Plasma includes in the kwineffects header seemed to pull in
quite some additional headers, so the includes in some effects have
to be adjusted (most often KConfigGroup). This should speed up the
compilation of the library and the effects.