Use Device.js to determine mobile editor use

Ref #2570
- Adds new library, device.js to determine if the user is on an ios mobile
  or tablet.

### Needs Testing

I don't actually own any iDevices! I made this PR so that my touchscreen laptop would stop giving me the dumbed down editor ;)
To that end, if anyone with an iDevice could pull this down and confirm that they continue to get the dumbed down version, I'd appreciate it.
(You can tell you have the mobile editor because your markdown doesn't highlight)
I actually meant:
`if (device.mobile() || (device.tablet() && device.ios())) {`

CodeMirror doesn't work on any mobile as far as I know.