Need the ability to remove a counter

[rofrano]

As a User
I need a way to remove a counter from the list
So that it no longer shows up in the list of counters

Assumptions:

• We can delete a counter in Redis

Acceptance Criteria:

Given that the counter `foo` exists
When I issue `GET /counters`
I should see `foo` in the list of counters
And I issue `DELETE /counters/foo`
Then the `foo` counter should be deleted
When I issue `GET /counters`
I should not see `foo` in the list of counters