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.
Merge pull request #519 from jasl/refund

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Merge pull request #529 from jasl/rename-changes

重命名Event和EventChange的关联为updates
merge master.
fixed rspec error.