Set auto-track on a per-dependency basis

[Caio Begotti]

When editing a project you should be able to set/unset "auto-track" for each dependency individually.

From https://github.com/capomastro/capomastro/issues/106

[Daniel Manrique (roadmr)]

This will need some UI changes. Interestingly, project and dependency are associated through a "ProjectDependency" model which is the one having the auto-track flag so it *looks* like the DB already has this in mind. The form (ProjectForm) "propagates" the single auto-track checkbox to all the dependencies, and is actually the only one that does it' there's no edit support for auto_track, seemingly.

I'll schedule this bug for a bit farther in the future because it depends on https://bugs.launchpad.net/capomastro/+bug/1419705. We need to know exactly what auto_track means before we can decide how important this is.