Add Voluptuous to validate the action parameters

We want a simplest way to validate the input parameters of an
Action through a schema.

APIImpact
DocImpact
Partially implements: blueprint watcher-add-actions-via-conf

Change-Id: I139775f467fe7778c7354b0cfacf796fc27ffcb2

watcher/db/sqlalchemy/models.py

@@ -160,7 +160,6 @@ class Action(Base):
                             nullable=False)
     # only for the first version
     action_type = Column(String(255), nullable=False)
-    applies_to = Column(String(255), nullable=True)
     input_parameters = Column(JSONEncodedDict, nullable=True)
     state = Column(String(20), nullable=True)
     # todo(jed) remove parameter alarm