Fix "<htmlstring> has no method forEach" error from JSGI

Whenever I hit a page that renders a view (via bogart_handlebars), I get this ugly error message in my console that says "<entirehtmlstringofmyview> has no method forEach".

This PR will add the `"content-type": "text/html"` header to the returned response, and make the body an array (following in the line of the `bogart.html` response helper).  This will silence the JSGI error.