Wip: Draw menu via QStyle
Right now we are just using a colored rectangle, which is ok with breeze but not with other styles.
- Overlap of submenus
- Color is wrong in Breeze because it uses a mix of Window and Base color but they are the same in palettes coming from Kirigami
- No gradient in Oxygen because it needs an actual widget for that (nothing we can do about that, if the style checks for a widget).
- Pixel artifact in Oxygen:
- Shadow (still need to hardcode)
- TODO: Separator
- Figure out a way to extend menuitems to the border of the menu
- Investigate missing space on the left of menu items