if a collection has no name, use a UUID on import

Fixes #1100838, some SUSE repositories don't have that name element.
Add support for extlinks and update intersphinx config

This commit adds support for extlinks, which has been used to condense BZ links
as well as link to documents in platform.

The intersphinx config has been updated as well to be called `platform` instead
of `pulp`. The `rtd_builder` var has been added to `conf.py` to point to the
correct `objects.inv` file.

Some sphinx build warnings have also been addressed.
Merge pull request #596 from beav/extlinks

Add support for extlinks
Updates for 2.5.1 becoming 2.6.0
Merge pull request #598 from bmbouter/updates-for-2-6-release-stream

Updates for 2.5.1 becoming 2.6.0
Merge branch 'bz_1100838' of github.com:ATIX-AG/pulp_rpm into ATIX-AG-bz_1100838
Adding 2.5.0 release notes
Merge branch 'release-notes' into 2.6-dev

Conflicts:
	docs/user-guide/release-notes/2.5.x.rst