Export current document JSON should return JSON content-type, not HTML

Selecting "Export current document JSON" opens a new tab with "json.html" with Content-Type: text/html. Semantically, I think this should actually show a JSON response (instead of HTML) so that other browser extensions can format the response (e.g. syntax colouring, folding, wrapping, etc.). There may be some value in having two links: "display HTML" (with current/improved styling) and "display JSON" (providing a pure JSON response), although I think most browsers display JSON responses directly anyway (and for those that want a configurable, formatted JSON display, they can use an additional extension).

(Note; I'm using BDE version 2.1.1, but the "Affects Version/s" field below only goes up to 2.1.0 ...