Group Policy Mapping API-1: EP, EPG, L2 Policy, L3 Policy

(Patch series identifier: GPM-API-1)

This patch extends the initial set of Group Policy API resources with
attributes mapping those resources to traditional Neutron
resources. Subsequent patches will add the DB, plugin, and driver
support for these mapping attributes.

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

Change-Id: I617efd632f6ca423b58f2e9ba504cf6c4bc2ac53
Merge "Group Policy Mapping API-1: EP, EPG, L2 Policy, L3 Policy"