Release Zulip Server 1.6.0.

Release Zulip Server 1.5.2.

Release Zulip Server 1.5.1.

Release Zulip Server 1.5.0.

Update changelog for Zulip 1.4.3 release.

Update changelog for Zulip 1.4.1 and 1.4.2 releases.

Upgrade: revert change to default LOCAL_UPLOADS_DIR in prod settings.

The main purpose of the "var" convention is to make it easy to write stuff
inside of our git repo when running a dev instance, and then "var" gets
excluded from checkins. For production, that's not as much of a concern.
For upgrades we don't want to be changing the directory around and confusing
matters, especially with the extra moving part of nginx configs (which have
their own issues in terms of being overwritten by accident when admins go to
S3).

Release Zulip 1.4.

Add changelog for Zulip 1.3.13 release.

Add changelog for Zulip 1.3.12 release.