[FEATURE] Implemented "Delayed Stroke" feature for brush smoothing

This patch adds two improvements to the Stabilizer algorithm implemented
by Juan Luis Boya García:

1) "Delayed Stroke" feature. If enabled the brush has a dead zone, where
   nothing is painted. This is extremely handy when one needs to paint
   a smooth line with explicit angles.

2) "Finish line" option for the brush stanilizer. When option is disabled,
   the line will not jump to the cursor position in the end of the stroke.

CCMAIL:kimageshop@kde.org