Wagtail-events

With this release:

- Fixed bug stopping EventIndex page from being added to a parent, even the site root or home page, within the wagtail admin.
- Events are added to the wagtail explorer sidebar for quick list/create shortcut
- Wagtail Homepage shows a number of events overview
- Package details including readme updated to display correctly on pypi
- Fixed need to import package to get __version__ when parsing setup.py
- Templates and static files are correctly added to the package

- Updates for code style guide compliance
- Fixed date range filters to provide a valid queryset as a response from EventIndex._get_children()

A major refactor away from the original library, to simplify the nature of the events model. Using an event series with many dates just made things more complicated than they needed to be, so now we rely on singleton events, which inherit from wagtail Pages.

Abstract models are given more capability - in particular, the AbstractEvent is designed so that the event functionality can be neatly inherited by a model in a third party app, redefining all the nonessential fields (description, image, etc) without having to duplicate core functionality.