Added the following FIXME:
How should a Twitter user get their Inbox filled with foreign tweets?

Every imported Twitter user has a profile in the Profile table, so we
could setup a Subscription entry for each of those, meaning they get
collected in the InboxNoticeStream... But this would mean a lot of
unnecessary entries and listings that generally just point to the
locked down Twitter service.

Let's figure out a good relation so we can connect any profile to any
imported foreign notice, so it shows up in the "all" feed.