Added oslosphinx theme & enabled the incubating theme

Added via -f <url> as per https://wiki.openstack.org/wiki/Oslo#Why_aren.27t_alpha_releases_of_oslo.config_published_to_PyPI.3F

Change-Id: I4e35abd6da42a5d9a7bb8c3b56fd4e8610e4e17c
Merge "Added oslosphinx theme & enabled the incubating theme"