This fixes federation with Mastodon instances that have Authorized
Fetch turned on by signing the GET request to fetch the actor when
a blog is first followed.
Ref T820
This renders all requests for that user's posts, collections and related
ActivityPub endpoints with 404 responses.
While suspended, users may not create or edit posts or collections.
User status is listed in the admin user page
Admin view of user details shows status and now has a button to activate
or suspend a user.
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
Matt Baer
Rob Loranger
Michael Demetriou