Make my_order filters more flexible

@mikejolley added action hooks for buttons in #2704 to the my_account / my_orders. This pull also adds them to the status links and updates his changes slightly.

1) It makes the order status links filterable. For subscriptions, I want to the flexibility to remove the 'Cancel' link on failed orders without requiring custom templates.
2) I added text keys ('cancel', 'pay', 'view')  for each item which makes it easy to 'unset' in the filter rather than having to do some sort of search (especially since it is impossible to search a translated string). For example, I want to unset the 'pay' button for failed subscription renewals that have already been paid in another order.
3) I changed the sanitize_title to sanitize_html_class which seems more appropriate.