There are no longer two separate projects living inside the horizon
repository. There is a single project now with a single setup.py,
single README, etc.

The openstack-dashboard/dashboard django project is now named
"openstack_dashboard" and lives as an example project in the
topmost horizon directory.

The "horizon/horizon" directory has been bumped up a level and now
is directly on the path when the root horizon directory is on
your python path.

Javascript media which the horizon module directly relies upon
now ships in the horizon/static dir rather than
openstack-dashboard/dashboard/static.

All the corresponding setup, installation, build, and env scripts
have been updated accordingly.

Implements blueprint unified-packaging.

Change-Id: Ieed8e3c777432cd046c3e0298869a9428756ab62