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/db/sqlalchemy/models.py

@@ -138,6 +138,7 @@ class Goal(Base):
     uuid = Column(String(36))
     name = Column(String(63), nullable=False)
     display_name = Column(String(63), nullable=False)
+    efficacy_specification = Column(JSONEncodedList, nullable=False)
 
 
 class AuditTemplate(Base):