add event order participant model.
send sms to user after participant record create.
update settings.yml.example
send checkin code to user after paid.
hide user checkin button.
fixed checkin index page error.
remove old participant model.
fixed event change error.
remove checkin and join business.
remove checkin and join files.
add migration from event participant to order participant.
rename event changes to updates, cause that naming conflicts with rails model
fixed migration error.
use let! instead of let.
merge master.
don't send email when migrate data.
refector using state_machine
add EventOrder status transition logger
clean up
move priceable gem into lib and hack it to solve conflict with observer