Set kdecoration and kstyle bias_default to 0.2
Sets the KDecoration and Kstyle bias_default values to 0.2 as discussed here: teams/vdg/issues#38 (comment 865705)
Also refactor Kdecoration to calculate values instead of hardcoding them
Merge together with frameworks/kirigami!1463 (merged)
Edited by Akseli Lahtinen