Enhancement: empty instance.js file & jquery clean up

ref. to https://github.com/Codiad/Codiad/issues/378

- Removed unused jquery version (was there any reason why we need that?)

- Is it possible to add an empty instance.js file to index.php? Makes it much easier to maintain demo and doesn't hurt anyone. If this is merged, Hosters can hook in very easily without any modification on the core and apply restrictions.