On workboards, link ancestor project breadcrumbs to their workboards

Summary:
Ref T13269. Currently, if you're on a milestone workboard like this:

Projects > Parent > Milestone > Workboard

The "Parent" link goes to the parent profile. More often, I want it to go to the parent workboard. Try doing that? This is kind of one-off but I suspect it's a better rule.

Also, consolidate one billion manual constructions of "/board/" URIs.

Test Plan: Viewed a milestone workboard, clicked the parent link, ended up on the parent workboard.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13269

Differential Revision: https://secure.phabricator.com/D20331