Fix abstract fields not showing up in the book

* Also, show and hide them according to the settings
Fix event arrival dates when start_time > end_time
Timetable arrows shifted when less than 20 mins
Code simplification and visual improvements
Wording - 'Edition' -> 'Edit'
Nicer HTML color -> RGB conversion function

Properly handles 3-digit hex codes too.
PEP8/style fixes
Init files for events module
Create event model for indexing
DB migration for event indexing
Implement ConferenceIndex
remove unused code and PEP8 refactoring
Adjust code to reflect new index API
Create categories module
Add migration changes for categories index
Rename table events to events_index
Implement CategoryTitleIndex
Adjust code to reflect new categoryTitle index API
Add initialize methods
Remove useless code for Whoosh indexing