Ensure `get_base_url()` does not include a trailing slash.

Clean up a few other URLs and add tests.

Closes #274.
Set vintage year, not whole date.
backend: Add and emit signals.
Disable local user editing in embedded mode.
Add registration_mode and Invitations.

Issue #249.
plugins: Hide plugins which lack admin settings.
kegadmin: Split settings into multiple views.
Invitation support; registration rewrite.

django-registration views are no longer used.

Issue #249.
Drop obsolete registration fields.

Issue #249.
Suppress missing URL when printing backup.
Update template for `registration_mode`.
v0.9.31
Fix staff-only invites: `is_staff` is not a function; add tests.
v0.9.32
Make keg images clickable.

The "clickable" js (in skel.html) avoids existing `a`
and `img` entities.  There's probably a better way to do
that in general.

Closes #280.
Ensure prior stats is a dict.
webhooks: Post full event data.

Issue #276.
Fix regression in registration form: properly validate fields.

Issue #283.
Update changelog
Bump Celery/Kombu versions now that upstream issue is fixed.