Django-spectator

- Ensure works with Django 2.1.
- Change to use pipenv for managing devproject dependencies.
- Add `spectator.reading.utils.annual_reading_counts()` method.
- Add 'Books' and 'Periodicals' tabs to Reading Year Archive pages.

- Upgrade Django used in devproject to 2.0.5.
- Upgrade Bootstrap from v4.1.0 to v4.1.1.

- Add missing migration.

- Undid/simplified some of the previous date-related settings; needs more thought.

Core

- Remove leading `www.` from visible display of domains when URLizing them.
- Better handle default settings.

Reading

- Add optional settings to customise the format of dates when displaying Readings.
- Stop possibility of a Publication appearing more than once when listing Publications being read on a specific day.
- Order in-progress Publications by when they were started to be read.

Events

- Turn Exhibitions into a new kind of Work:
- Renamed `"exhibition"` Events to be `"museum"` (Museum/Gallery) Events.
- Added `"exhibition"` as a new Work kind.
- Added a migration to add an Exhibition Work to every Museum/Gallery Event, and move any Creator(s) over to that Work.
- Add optional settings to customise the format of Event dates in templates.
- Display the number of Events on a Venue detail page.

- Add `Creator.get_events()` method for more accurate counting.
- Fix bug with counting Events or Works multiple times when counting a Creator's Events/Works and they had more than one role on an Event/Work.
- Add counts of Venues and Movies/Plays/etc on their list pages.