"More Effects" dialog work:

1. Don't resize the dialog when changing effects. It turns out you need no code to do this!

Remove bogus code that actually resized the dialog.

2. Introduce kpTransformPreviewDialog::setUpdatesEnabled() and use it to reduce the number of preview pixmap recalculations from 2 to 1 when switching effects. Also try to use it for reducing the number on kpEffectsDialog ctor construction.

3. Reduce number of preview pixmap recalculations by adding <defaultSelectedEffect> arg to kpEffectsDialog ctor, removing the need to call kpEffectsDialog::selectEffect() afterwards.