Integrated DSE, Data sources, and Policy engine

Previously, the policy engine had no way to communicate
with the data sources.

This change integrates the policy engine and all the
data sources into the DSE framework.  This change
does not ensure that the datasources are periodically
updated and deltas sent on the message bus.

Change-Id: I725f65991b8436da5d51dea702c5456cb80380aa