6.0 Release Notes -- New Features Partial

This CR includes the front matter for the Release Notes
plus some of the new features.

The following New Features are covered in other CRs:

- Multiple Cluster Networks -- in the CR for that feature.
  (the l2-multiple file here is vestigal and will be replaced)
- Multiple L3 Agents -- in the CR for that feature

- Pluggable Architecture -- https://review.openstack.org/#/c/143025/

- Partner provided technologies -- https://review.openstack.org/#/c/143025/

The contents of New Features has been modularized to give us
more flexibility and enable us to better xref the main docs
from the Release Notes.

All experimental features are now grouped together.

Change-Id: I2cf0595689ac6fb99bd4a67a03b92840c29e4638
Merge "6.0 Release Notes -- New Features Partial"