Log Message:
graphics/kvantum: update to 0.20.0

Main changes:
- Fixed drawing of view-items with right-aligned decorations.
- Added an option for always centering normal tabs (in contrast to the document \ 
mode).
- Added an option (to Kvantum Manager) for styling vertical toolbars.
- Fixed a small problem in tab overlapping.
- Don't allow kinetic scrolling inside subwindows.
- Used version check for KWindowSystem because of method deprecations.
- Dropped support for Qt5 < 5.12.