Add Event types

Close #39. Close #38. Close #36. Close #35. Close #30. Add event types. Update events to work with event types. Add tests for event types. Update event tests.
When an event type is updated I don't know how to replace the old one with the new one using a partial maybe:
`$("#event_type_<%=@event_type.id%>_name").html("<%= j render partial: 'event_types/event_type_detail', locals: { event_type: @event_type} %>")`