Edit section for dependent campaigns
In the Compose Campaign screen, we need to have a thingie to let you
add CampaignDependency items that attach this campaign to other campaigns,
along with a file-pattern-match for what output files from the previous
campaign we want (default "%" for match-any).
It might be nice to show what we depend on as well as what depends on us(?)
and let you edit either list.
Even fancier, it could show the whole dependency graph of any related campaigns...