Main changes:
● Reset widget palettes on changing style from and to Kvantum. This fixes several problems with on-the-fly style changes, so that an app restart won't be needed in most cases of style change (which shouldn't be mistaken with Kvantum theme change).
● Added an option to Kvantum Manager for enabling window translucency with non-integer scale factors after showing a warning.
● Fixed the height of combo menu separators (they were too big).
● Updated the code for Qt 5.15 backward compatibly.
● Added a workaround for a regression in Qt 5.15, which results in QStyleOptionTab reporting an incorrect tab position.