Add IdP management extension (Federation pt1)

Add an extension to manage IdPs, this is required for adding federation
support to keystone.

Co-Authored-By: Kristy Siu <kwss@kent.ac.uk>
Co-Authored-By: David Chadwick <d.w.chadwick@kent.ac.uk>
Co-Authored-By: Joe Savak <jsavak@gmail.com>
Co-Authored-By: Marek Denis <marek.denis@cern.ch>
Co-Authored-By: Dolph Mathews <dolph.mathews@gmail.com>

Implements: blueprint virtual-idp
Change-Id: I783d85748d4c051ee685a5b54a824a7d461e1860
Merge "Add IdP management extension (Federation pt1)"