We need to determine what happens when such a comment is successfully
posted, as we can't just reload the comment list. In other words, this is
dependent on where we are embedded, and cannot be handled just locally.
- Comments are stored in HTML as well as Markdown, so that conversion
only happens when saving (rather than when viewing).
- Added 'markdown' Jinja filter for easy development. This is quite
a heavy filter, so it shouldn't be used (much) in production.
- Added CLI command to update schemas on existing node types.
