Interactive (e.g. navigation, attribution) element have z-index 10.
Overlayed elements (slider, route bubble) have z-index 20.
Filling elements have z-index -1 to 9.
Cover have z-index 100.
Special elements (debug) have z-index 50.
Do not change z-index in server cssnano plugin (z-index are not
changed when built from npm script).
Add slider visible configuration value to make it
controllable.
Render slider with DOM renderer.
Indicate on slider state if DOM or GL needs render.
Subscribe to DOM renderer element to get element
and add event listener by creating observable from
event.
Create non styled slider when enabled.
Disable prevent default in mouse service to recieve
input events.
