Feature/server checkin handler

- Created new helpers.js file to house db update functions
- Updated schema to include new checkin_time column in events_participants
- Added new package moment.js for date manipulation
- Updated dummy data to include at least one deviceID for testing
- Fixed bug in dummy data years for january events
- Created checkinUser function
---- Takes a deviceID as an input
---- Grabs the correct participantID
---- Grabs the event that's closest in time to right now
---- Checks if they are late or on-time
---- Updates the db with both their status and their checkin time