Archive repositories when sending a DELETE to the repository resource.

Review Request #10374 — Created Jan. 3, 2019 and submitted — Latest diff uploaded

Review Board

We've had support for hiding repositories through the API by issuing
HTTP DELETE requests to the API resource since the 1.6.x timeframe.
After that, archiving of repositories was introduced, which the API
gained support for through a PUT with archive_name=1, which worked but
probably should have been done through a DELETE request.

Now, when performing a DELETE, we archive the repository instead. This
has the same general effect as what we had before, with the benefits
that the repository name could be reused afterward.

Unit tests pass.