New [up|down|stop]_disabled_states config to control button disabling

[scarey]

This would be used instead of disable_end_buttons since it allows finer control. The config could look something like:

    up_disabled_states:
      - open
      - opening
    down_disabled_states:
      - closed
      - closing
      - opening
    stop_disabled_states:
      - open
      - closed
      - closing
      - stopped

[scarey]

I think this would help issues #22, #46, and #96.