Basic structure of the freezer web ui integrated in horizon

This commit add to the repo the basic structure of the web ui
integrated with Horizon. There currently nothing under the Freezer
tab, this is only a base point to start to develop the Freezer
ui content.

Basic installation instructionr are available in the file
horizon_web_ui/README.rst

Change-Id: I6e1ef399c869494ec1c5c9dd52a6d9adfd9360c9
LAUNCHPAD: https://blueprints.launchpad.net/freezer/+spec/horizon-webui