Allow Markdown within the speaker bio and proposal abstract,
with a restricted set of tags for safety.
Render direct to markdown instead of storing plain and HTML
in the database.
Fix issue in timetable when a day had no slots created.
Upgrade site and modules to Django 2.2. Remove and replace obsolete
functionality with current equivalents. Update requirements to latest
versions where possible. Remove unused dependencies.
Boot custom CSS, and put some base, standard css in its place.
Shame I did not start with fresh Bootstrap4, but oh well.
Some more templates could be made to make this less messy, which would
be good.
