Releasing pretalx v0.3.0

As the first pretalx release in 2018, we're introducing pretalx v0.3.0, with some features, and some bug fixes.

Features

Speakers can now be marked as "arrived", helping you see when somebody is still missing shortly before their talk.

Attendees can now download an ical file containing all talks of a single speaker, which will also be helpful for
speakers themselves.

We added API endpoints with information regarding speakers, and generally provide more information in various API
endpoints, for example speaker biographies, and answered questions.

Bug fixes

• Non-superusers could not access the email sending form.
• More than one event stage could be shown as active in the event overview dashboard.
• Trying to look at entered submissions without being logged in produced a server error instead of a 404.
• If notifications about new submissions were turned on, they were sent to the submitter instead of the organizer.