Add ability to delete a counter

[rofrano]

As a: User
I need: the ability to delete a counter
So that: I can remove unwanted counters

Assumptions:

• Deleting a counter will remove it from the database
• If the counter doesn't exist a 204_NO_CONTENT will be returned

Acceptance Criteria:

Given I have counter named foo
When I delete the counter named foo
Then I should receive a 204_NO_CONTENT
And I retrieve the counter named foo
Then I should receive 404_NOT_FOUND
And I delete the counter named foo again
Then I should receive a 204_NO_CONTENT