Rename event order status.

- request_refund -> refund_pending
- complete_refund -> refunded
Use PUT instead of GET to cancel/refund for security.

GET should be for only read only requests.
Add Timecop to fix time related rspec failures
Add User#ordered? to check whether user has ordered the event.
Show link to orders page if user has already ordered the event.
Use redirect_back_or to keep event filter in user orders page.
Allow filter user orders by event id.
Show info if user orders page has been filtered.
Merge pull request #531 from doitian/event-order-refactoring

Rename order status and replace GET requests with PUT.
Update alipay gem version.
Merge pull request #534 from chloerei/master

Update alipay gem version.
Merge pull request #532 from doitian/492-user-event-order

Show button to let user check orders for the event.