Theming: Create hover/active state for icons in new themes

The two new themes remove the background effects of hover states and active states from the mode bar (and of hover states from toolbars). Instead, the hovered/active icons have a mode pronounced color:

This needs to implemented in a way that does not require modifying all icons. Also, it must not have an effect on the other themes which still use the background color for hover/active state visualization.