Add counter component

[fabaff]

Description:

This PR is based on the idea of #6880 and uses the same configuration variables. It is not a sensor but a component now and still provides increment, decrement and reset as a service for automations.

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#3250

Example entry for configuration.yaml (if applicable):

counter:
  count1:
    name: Count1
    initial: 10
    step: 3
  count0:
    name: Count0
    icon: mdi:baby-buggy

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[mention-bot]

@fabaff, thanks for your PR! By analyzing the history of the files in this pull request, we identified @pvizeli, @konikvranik and @postlund to be potential reviewers.

[pvizeli]

I think instead to have a counter we should make a timer component with a nice UI card. For timer we can also make dynamic timers that can be create and delete and change on runtime. The state if a timer is run/stop/pause and fire a event on zero. That help to not make a state to db every time where the counter change like this

[fabaff]

This component doesn't not depend on time. If I understand your comment right then you are talking about something like a countdown from 10 min and then do something.

Incrementing and decrementing happens when the service is executed. Like do something for x times while you know that after x+n times you have to replace the battery, so show a notification when x+m is reached.

[pvizeli]

Okay, now is clear, thanks