A little bit debug information about the current keyboard state is
useful. Thus a new tab is added to show information about xkbcommon.
It shows:
- layouts in the keymap
- currently active layout
- supported modifiers in key map
- currently active modifiers in state
- supported leds in key map
- currently active leds in state
Whenever a key is pressed/released the complete ui is updated to reflect
the latest state. That is pressing/releasing a modifier is directly
reflected in the ui.
This UI can extended as needed for further debug information about the
keymap state.