Show dependent roles in the UI

[adamnfish]

Recipes only show explicit roles in the UI. It should show dependent roles as well as those that are present by virtue of being in the provided base image.

[cb372]

This information should also be shown on the edit page for a role.

e.g. if role foo depends on role apt, and you check the checkbox for foo, then the checkbox for apt should be automatically checked and greyed out.

[kenoir]

This has the knock on effect of making variables in dependent roles assignable only through the parent role which is a bit confusing.