add refunding and refunded status
remove canceled_at
add user refund link
merge master but ruby&js code has 2004 lines greater than 2000
pending >2000 spec
improve by suggestions
rename
merge master
clean up
rename event changes to updates, cause that naming conflicts with rails model
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.