Import Sphinx theme for OpenStack

This is a copy of the Sphinx theme for OpenStack developer
documentation imported from the ceilometer repository. After
this library is released, we will remove the copies of the
theme from all of the other repositories.

blueprint oslo.sphinx

Change-Id: I20b6c224b8d8fbede354c2a28ad67eda3a4b9dac
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>