This PR depends on #106

Changes

CalendarEvent now has a status so that the event's timeslot can show as 'Busy' or 'Free' in calendar clients
EventExtractor:
- Status customisable per extractor
- Location can be customised as well
Improve the ics.js to support our CalendarEvent when adding new events.
Options page:
- Fix some UI glitches, such as the sidebar not taking the full page height, resulting in a random whitespace in the bottom.
- Remove 'dead buttons' that were never implemented (for resetting all fields. I think it is nice little touch and is scheduled for v4.3, https://github.com/msramalho/SigTools/projects/3)
- Support for <select> input elements, needed for events status (which is enum type).

Preview

Sidebar with icons and human readable names for extractors: