Operator shelf edit form (bug 1074431)

r? @ngokevin @cvan @spasovski 
Some of the fields use the enter key for non-submission things, so it's suppressed, e.g.

https://github.com/mozilla/transonic/blob/97bf618a9add6dceb62c0f06a30fa5304b75f7c6/src/media/js/fields_transonic.js#L9-L13

I agree that it's not awesome, but I'm mostly extracting transonic code for this project :/