Django-spectator

- If the end reading dates for all publications on a year archive page only have year granularity, don't show the months (which was always "January").
- Add `loading="lazy"` to thumbnail images in lists (only works on Chrome).
- Fix sort order of names that end with parentheses like "Sam Taylor (1)".

- Increase thumbnail JPEG quality from 60 to 80.

- Add two ImageFields for uploading images: `Publication.cover` and `Event.ticket`.
- Now installs [ImageKit](https://django-imagekit.readthedocs.io/en/latest/) (which needs [Pillow](https://python-pillow.org) or [PIL](http://www.pythonware.com/products/pil/) to be installed first).
- Publication cover images are displayed in a publication's detail template, and in lists, but not in the sidebar cards. Also in the Admin.
- Event ticket images are displayed in an event's detail template and in the Admin.
- There are new settings (with defaults) related to these images: `SPECTATOR_THUMBNAIL_DETAIL_SIZE`, `SPECTATOR_THUMBNAIL_LIST_SIZE`, `SPECTATOR_EVENTS_DIR_BASE` and `SPECTATOR_READING_DIR_BASE`. See the README for more details.

- Update included Bootstrap CSS from 4.1 to 4.3.

- Ensure works with Django 2.2.
- Stop testing in Python 3.4 and/or Django 2.0.

- Stopped HTML tag appearing in the `title` tag of Event Detail template.