Add Mingle.updateCard method

* Adds Mingle.updateCard method
* Makes Mingle.addCard return card location API URL
* Updates entity/id handling to ignore unicode->str conversion errors
when prepping data as card props
* Use Mingle.updateCard to set card status

Note that this should ultimately be updated to make Mingle.updateCard
take a card number, rather than API URL (and have Mingle.addCard return
card num rather than API URL)
Merge branch 'master' of github.com:awjrichards/bingle