Add support for showing current position for covers

[jonasjeeliasson]

Kept _renderCircleState default behaviour to use brightness for any type of entity, except for the new functionality for covers.

Examples with statePositionTop = true:

Example with statePositionTop = false:

[mattclair]

Not exactly what you are requesting, but this can be accomplished.

icon: mdi:garage
offStates:
  - closed
offIcon: mdi:garage-closed

[jonasjeeliasson]

Not exactly what you are requesting, but this can be accomplished.

icon: mdi:garage
offStates:
  - closed
offIcon: mdi:garage-closed

Yeah that I figured out, it was used to generate the screenshots in the description as well :-)

What this PR adds is support for showing the precentage as well.