Policy proposal for partner repository

[Allison Randal]

Thanks all for the work on reviewing and improving this policy. It's 
substantially better for the effort, and I'm glad we managed to merge 
for ARB and commercial as well (both were in the process of similar 
efforts at documenting the policy, so we caught 3 birds with one stone).

I've renamed the wiki page to reflect the new more general nature of the 
policy, and noted the tech board's approval:

https://wiki.ubuntu.com/ExtensionRepositoryPolicy

We'll work with the archive admins to get this linked in from the 
appropriate places.

Allison