Optimize database performance of the footer API

[davidfischer]

Currently, the number of database queries in the footer API depends on the number of versions of the project in question. This optimizes the API to always be a constant number of queries.

This PR partially fixes #3712 in that it fixes the major performance issues with the resolver when generating a number of URLs for different versions of the same project. Currently project.ordered_active_versions is only used by the footer API but anywhere else looking to generate URLs for a list of versions could use that function to get the same performance benefits.

The test case does seem a little bit brittle but I'm not sure what the best way to improve that is.

[ericholscher]

Solid improvement! Will be curios to see how this improves performance on the footer API. I wonder if it's worth another PR to add these improvements to the version listing page, at the least?

[davidfischer]

Will be curios to see how this improves performance on the footer API

This should be a large improvement but it's hard to say exactly how large it will be because footer API calls with 1-2 versions won't be improved as much.

I wonder if it's worth another PR to add these improvements to the version listing page, at the least?

That's a good idea.

[ericholscher]

Gonna ship this today.