Releasing pretalx v0.5.0

Only two weeks after the last release, we present pretalx v0.5.0, with a long list of features, most prominently a
Plugin API!
We'd like to thank our contributors Jahongir Rahmonov, Michael Lutonsky, and Raphael Michel for their ongoing
contributions, as well as our first time contributor Thies Müller.

Update notes

This release changes the postgreSQL dependecy psycopg2 to the now equivalent psycopg2-binary. If you're using
postgreSQL, please uninstall psycopg2 (pip uninstall psycopg2) and install psycopg2-binary.

Plugin API

This release also introduces the beginnings of a Plugin API – at the moment, you can register custom data exporters,
custom URLs, and even add entries to the organiser area navigation sidebar! Head over to our developer documentation
if you're interested.

More plugin hooks are going to be introduced in the coming releases – if you have anything you'd like to see as a plugin
in pretalx, tell us about it!

Other Features

• Organisers can now decide if reviewers should be required to submit a score or a text with their review.
• Organisers can provide room-based information for speakers, which will be provided in emails about talk scheduling.
• Speakers can now upload an image that will be displayed next to their talk information.
• Reviewers can now also be asked custom questions during their review, with all capabilities that speaker questions have.
• There are now optional review deadlines, preventing reviews to be added, modified, or removed after a certain date.
• Organisers can now show information snippets, including files, to submitters, or speakers.
• More environment and configuration variables were added to support customisation of filesystem decisions.
• UI improvement: Submission status can now be changed via a drop down instead of action buttons, making it easy to
  transparently change the status of a submission arbitrarily.

Bug fixes

• In the dashboard, an incorrect link was given to add new reviewers.
• The "save" button was missing on the mail settings page.
• Users could not see (instead not change) their submissions after CfP end, until they were either rejected or accepted.
• In the \<title> tag, the event was displayed twice, once properly and once in a technical representation.
• Documentation fix: The environment variable for database passwords is PRETALX_DB_PASS, not PRETALX_DB_PASSWORD.
• Unconfirmed talks showed up as empty boxes in the schedule editor.
• Upgrading the privileges of an existing user did not result in an email, since no invitation was required.
• The Docker setup was broken. It is fixed, and a notice of limited support was added to the documentation.
• The orga view now always uses the event timezone.