Add ability to tap on slider and trigger custom command whether slider is enabled or disabled

[lizsugar]

This one is a pretty big change and most of my PRs submitted after this one (e.g., scene domain support) work best if this is already merged.

This change is not backwards compatible. The previous slider.has_toggle option is replaced by slider.disable_sliding.

This allows the user to define a tap_action on the slider element independent of action button and icon. The tap_action fires whether slider can move or not and does not fire when the slider has moved.

Examples:

For switches

slider:
  disable_sliding: true
  tap_action: toggle

For lights

slider:
  disable_sliding: false
  tap_action: toggle

For media players

slider:
  disable_sliding: false
  tap_action: more-info

For scenes

slider:
  disable_sliding: true
  tap_action:
    action: call-service
    service: scene.turn_on
    service_data:
      entity_id: scene.dining_room_on