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>

In the current doc, the command examples are like
"os server create" but the acutal command should
be started with "openstack" instead of "os", it
is misleading to first time users.

Change-Id: I80c96f0938cec382f2f714a500138bd5a2c81aa0

This patch does the following things to transfer
"ip fixed add/remove" to "server add/remove fixed ip":
* Add new command "server add/remove fixed ip", and unit
  tests and doc.
* Deprecate "ip fixed add/remove" command.

compute/v2/fixedip.py is not removed because the arguments'
positions are different between the new and old commands.
* ip fixed add <network> <server>
  server add fixed ip <server> <network>
* ip fixed remove <ip-address> <server>
  server remove fixed ip <server> <ip-address>

Change-Id: Ica07ccf92a76c21fd5608ecaff86ff7c4d96f5a0
Implements: blueprint rework-ip-commands
Partial-bug: 1555990
Co-Authored-By: Dean Troyer <dtroyer@gmail.com>

Fix the 'ip floating' command documentation file name.
Add missing command list documentation for the 'ip fixed'
and 'ip floating pool' commands.  In addition, update the
command description and argument help to fix minor issues
and use consistent terminology.  And finally, cleanup the
Network command object formatting.

Change-Id: I0168891bc674c9f0d4df4062f7e93f497dc8fe6f