A Bunch Tell is now Musing Studio.

Now when we check for the user at certain times and find that the user
doesn't exist in the database, we log them out and send them back to
the home page.

From the writeas org on GitHub.

This updates signup.tmpl to include all supported OAuth methods and respect the new `DisablePasswordAuth` config value.

This adds any OAuth login buttons to the invite signup page, stores the invite code for the flow duration, and associates the new user with it once successfully registered.

It enables invite-only instances with OAuth-based registration.

This instructs search engines to not index invite links.

Ref T661

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

Some of the work needed to have the backend match user-facing wording.

Ref T661

From u.Status == UserSuspended to u.IsSuspended()

Ref T661

- update error messages to be correct
- move suspended message into template and include for other pages
- check suspended status on all relevant pages and show message if
logged in user is suspended.
- fix possible nil pointer error
- remove changes to db schema files
- add version comment to migration
- add UserStatus type with UserActive and UserSuspended
- change database table to use status column instead of suspended
- update toggle suspended handler to be toggle status in prep for
possible future inclusion of further user statuses

Ref T690

This uses the Invite fetched from the database to explain a bit more
about how the invite URL expires. It also reduces some space around the
input box.

Ref T690

Ref T690

Ref T690

This ensures we see a 404 page when looking up an invalid invite URL,
even if the user is logged in.

Ref T690

this adds a new page with instructions for sharing user invites

if a user clicks the link for one of their own invite codes they are
directed to a page with clear instructions for it's use.

if a user clicks another users link they are redirectec to their account
settings witha flash telling them they do not need to register.

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 includes:

- A new `user_invites` config value that determines who can generate
  invite links
- A new page for generating invite links, with new user navigation link
- A new /invite/ path that allows anyone to sign up via unique invite
  link, even if registrations are closed
- Tracking who (of registered users) has been invited by whom

It requires an updated database with `writefreely --migrate` in order to
work.

This closes T556