instead of updating it later. This is more correct behavior, prevents an
additional query, and ensures that potential collection-creation when
claiming posts also respects the default (which it didn't before).
Ref T675
This is the crucial part where the hostName is needed for federation and
API clients. This change at least lets us know when we mess up like this
so the issue is easier to catch in the future.
This moves `hostName` to the `Collection` struct, where it's needed. The
field is populated after successful `GetCollection...()` calls.
This isn't the cleanest way to do things, but it accomplishes the goal.
Eventually, we should accept the AppCfg to `GetCollection...()` calls,
or make them `App` methods, instead of `datastore` methods.
Ref T613
This helps with post importing and clients that want to support post
scheduling. It also changes how Collection.ForPublic() works, no longer
resetting the ID.
Closes T532
