2160 string edit

Implemented a string-edit windows (as briefly discussed in COUCHDB-2160): when the cursor is on a line that contains a JSON-String (possibly with encoded quotes / newlines), one can open a textarea containing the unescaped text. This can replace much of what the field-edit view of futon could do - and it should help a lot with editing javascript for design docs or e.g. Angular with couch (when the code is actually contained in documents). Feedback is highly appreciated!
Is it not possible to make this css a class we just add to the `.string-edit` when we show or hide it?