Version bump and changelog for 0.18.3

changes/changelog.d/null-position.bugfix

-Fixed a crash when federating a track with unspecified position

changes/notes.rst

@@ -5,16 +5,3 @@ Next release notes
 
     Those release notes refer to the current development branch and are reset
     after each release.
-
-
-Avoid mixed content when deploying mono-container behind proxy [Manual action required]
----------------------------------------------------------------------------------------------
-
-*You are only concerned if you use the mono-container docker deployment behind a reverse proxy*
-
-Because of `an issue in our mono-container configuration <https://github.com/thetarkus/docker-funkwhale/issues/19>`_, users deploying Funkwhale via docker
-using our `funkwhale/all-in-one` image could face some mixed content warnings (and possibly other troubles)
-when browsing the Web UI.
-
-This is fixed in this release, but on existing deployments, you'll need to add ``NESTED_PROXY=1`` in your container
-environment (either in your ``.env`` file, or via your container management tool), then recreate your funkwhale container.