[feature] Improved service logic & Unit tests

Moved status verification from directive to service logic
Verify by status if subscription is valid (green text) or not
Wrote Unit tests to check that service responds correctly to API responses

@tejohnso I've refactored the directive as per your suggestion. The service will now verify what the status is and define whether to show either red or green text as per the requirements.

Could you, @donnapep or @stulees please review? Thanks.