Follow-up to ce9971b — the logo was only fixed in index.html.
Now profile.html, admin.html, and shared.html also wrap their
logo elements in <a href='/'> links.
Fixes#97
The profile page checked user.auth_provider to hide the password
form, but the backend doesn't return that field. Now also queries
/api/auth/oidc/providers and hides the password section when
password_login_enabled is false.
Fixes#96