Added efficacy specification to /goals

In this changeset, I added the new Efficacy, EfficacySpecification
and IndicatorSpecification classes which are the main components for
computing an efficacy.

Partially Implements: blueprint efficacy-indicator

Change-Id: I3a1d62569de2dd6bb6f9a52f6058313fa2b886ce

watcher/tests/db/utils.py

@@ -151,6 +151,7 @@ def get_test_goal(**kwargs):
         'created_at': kwargs.get('created_at'),
         'updated_at': kwargs.get('updated_at'),
         'deleted_at': kwargs.get('deleted_at'),
+        'efficacy_specification': kwargs.get('efficacy_specification', []),
     }