Added rake tasks and models for importing EventBrite dataq
Added a task to list the events on EventBrite
Added specs for listing of EventBrite models
Added more specs for the Eventbrite::Event model
Added task to import an eventbrite event
Added specs for EventBrite::Venue
Made date/time tests less fragile
Add Eventbrite::Importer for attendees of a specific event

Couple of changes:
- moved Importers folder to lib
- added Attendee importer
- made some basic changes to Attendee and Ticket model to deal with eventbrite data
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