Intersphinx linking

Intersphinx linking

each project now has its own read the docs page

example:
https://onap-oom-offline-installer.readthedocs.io/
this will redirect to the subproject location
in this case:
https://onap-doc.readthedocs.io/projects/onap-oom-offline-installer/

Added a new section on the main page:
active-projects
it shows linking in action.

you can click through to the subproject docs from there.
you will land on genindex.html
This is not ideal

To see why this is the case you can run
python -m sphinx.ext.intersphinx
'https://onap-doc.readthedocs.io/
projects/onap-oom-offline-installer/en/latest/objects.inv'

refer to https://gist.github.com/Aricg/27c739da7c35d201e9ca034df6e30ef6
we must link to one of the avaliable std:label

This means that each project should add a lable to its main
index page so that we can propery link it.

eg, in their index.rst add
.. _projectname-mainindex:

or something we can agree on.

Issue-ID: CIMAN-33
Signed-off-by: Aric Gardner <agardner@linuxfoundation.org>
Change-Id: I0e1b506d113b9fbbcf2cb854482dfb557d8012b7