Revised file processing screens on the backside of miniLock

Here is an implementation of the human interface design mentioned in issue #42.

And 3 videos that show it off:

Alice encrypts passport to Bob
https://vimeo.com/101773171

Save a secret song for my parents
https://vimeo.com/101773412

Crazy Town
https://vimeo.com/101773420
Sure. It would be better all around if miniLock.UI.fileOperationHasFailed received the error object from the worker. I didn’t want to make too many changes to the worker so that’s why I was matching on the error string.

Using a worker onerror handler allows us to access the error object which was thrown. And then that error can be passed to the callback so that we don’t have jank around with the message string. And doing so would be a welcome change in #55. I can do there while I bring it up to sync with master.