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

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.

instead of linking to posts only on a user's blog.

Ref T681

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

Previously, our hashtag parser would indiscriminately replace
hashtag-like text with hashtag HTML -- including in places it shouldn't
have, like inside code blocks. Along with the v1.7.0 changes to
writeas/saturday, this fixes that and closes #6.

As a bonus, strings of #spaceless#hashtags#in#a#row are now rendered
correctly.

Previously the logic was mixed up -- multi-user blogs would always load
collection number 1.