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!
This is just a personal taste and what we do in Fauxton. But could you make these variables only use one `var`. eg:

    var indent = editMatch[1] || "",
          hashKey = editMatch[2] || "",
          editText = editMatch[3],
          comma = "";