add event type to admin list of events
add event type constants to event model
reindex event_type for future use
helper to parse an event_type_str into something more defined
add migration utility to update event types
change how unrecognized event types are logged
add another matching string to district event types
store event types as enum values, more stringent checks for championship events
make use of event type_str
update comments
change event type property name for clarity
create /consts/ dir for EventType
forgot to commit new dir
Merge pull request #655 from fangeugene/event-type-1

Clean up event types -- Part 1
properly handle events without dates on team history pages. Fixes #663