A while ago desktop effects and compositing settings lived under the
but time has passed and now those two have their own kcms. This causes
- for newcomers it's harder to find code of the Desktop Effects KCM;
- git history doesn't look good, e.g. "[kcmkwin/compositing] Add some bugs to Desktop Effects KCM to fix later";
- in general, the mix of two doesn't look good in the code.
This change splits out the Desktop Effects KCM. Unfortunately, in order
to have more nicer code I had to refactor EffectModel a little bit.