This changes all variables and functions from using Suspend{ed} to using
Silence{d} as well as documentation, errors and logging.

(https://github.com/writeas/writefreely/pull/195#discussion_r334567408)

(https://github.com/writeas/writefreely/pull/195)

to the last because mastodon doesn't like

https://my.instance/@me but https://my.instance/users/me

be Note to work but I will open an issue for them and see what their
reaction will be.

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