Update our express.js settings.
Update our express.js settings.

* use app.set instead of disable/enable
* set Helmet CSP's `browserSniff` option to false; should be faster
* move `etag` setting along with the rest
* set `json escape` express.js' option to `true`
* set `json spaces` to 2

MaxCDN/bootstrap-cdn,MaxCDN/bootstrap-cdn,MaxCDN/bootstrap-cdn