Refresh, status and cancel enhancements

1. Addresses issue #4. A new parameter refresh_interval has been added to limit entity updates. When a zone is on, the count down timers "percent_complete" and "time_remaining" attributes update every second. HA records all these updates in the history which may or may not be a problem depending on your setup. The new default update time is 30 seconds. Please note that this does not affect any timings, only the screen updates, everything else is running as it should under the hood. If you are not interested in these attributes then increase this number further, perhaps to 60 to conserve resources. Set the value to 1 to have the same screen response time as previous releases. Nice values tend to be numbers evenly divisible into 60 (5, 10, 15, 20, 30).

2. Addresses issue #5. A status attribute has been added to the controller to better reflect the situation. Apart from on/off it also shows paused when between zones in a sequence.

3. Addresses issue #7. A new cancel service has been added to stop a currently running zone, manual or scheduled.