Implemented using a ColorModeMenu class,
derived from ToggleActionMenu (derived from KActionMenu),
as a child object of PageView.

* KToggleAction for every color mode, allows to set shortcuts for every mode.
  Color mode actions have icons.
* KToggleAction for normal colors mode.
* ToggleActionMenu containing all color mode actions.
  If triggered, toggles color mode between normal colors and last change colors mode.

"Toggle Change Colors" is replaced by "Change Colors", which is actually a toggle action.

BUG: 407217
BUG: 437755