This change adds tags functionality for projects in keystone. A user
can add a single tag with "--tag", chain "--tag" to add multiple
tags, or clear tags with "--no-tag".
Change-Id: I31cfef3e76dcefe299dacb00c11bb1a10a252628
Partially-Implements: bp project-tags
Move existing content around based on the doc-migration specification.
Replace :doc: markup with :ref: to have sphinx keep track of where the
files move and generate valid hyperlinks.
Add a few toctrees and index pages for the new directories.
Depends-On: Ia750cb049c0f53a234ea70ce1f2bbbb7a2aa9454
Change-Id: I253ee8f89d3ec40e39310c18bb87ed1d3d5de330
Signed-off-by: Doug Hellmann <doug@doughellmann.com>