Group Policy Model - Part 1

Introducing Group Policy API, and Resource Model with DB implementation. This
is the first in a series of patches which implement Group Policy.

Implements: blueprint group-based-policy-abstraction

Author:    Sumit Naiksatam <sumitnaiksatam@gmail.com>
Author:    Bob Kukura <kukura@noironetworks.com>
Author:    Stephen Wong <s3wong@midokura.com>
Author:    Mohammad Banikazem <mb@us.ibm.com>
Author:    Mandeep Dhami <dhami@noironetworks.com>