Add a timer entity

[pnsiva]

When using a timer entity. The multiple-entity-row card couldn't show the remaining time. Currently, it shows whether the timer is active or inactive. It would be nice if it could show "Idle" when idle, remaining time mm:ss while running, and mm:ss (Paused) when paused.

[pnsiva]

Another nice feature to add would be if you can pause, cancel or start any timer. I use multiple timers to turn devices on or off. It is very fitting to have them along with the associated devices.

[PavelD]

I have setup like:

- entity: timer.idle_timeout
  attribute: finishes_at
  name: finishes at
  format: time

I'm lucky that In this case it's ok for me to see just exact time, when time will timeouts but timer as format option will be great. It is more generic as you can use it for every timestamp/date value not only for timer entity.

Optionally is possible to use format relative, but I don't like much In xxx minutes string. Fortunately last ~40 seconds are updated every second.