Updating migration script and database dump to reflect schema changes.

1.  Please `git pull upstream master` into your `notes` branch and push to GitHub before merging this (so that you're merging on top of an up-to-date branch).
2.  This modifies `migrater.py` to insert empty strings for `notes` in `site` and `event`...
3.  ...and modifies `db.sql` to contain those strings.