Fix MP4 streaming issues

It happens to me quite often that an MP4 file does not stream correctly from my Raspberry PI to my tablet. It looks like it is an MP4 issue rather than an hardware issue.

Introducing Optiscroll.js

Optiscroll is a tiny (4kB gzipped, 9kB minified) and highly optimized custom scrollbar library for modern web apps. It aims to be as light as possible in order to not affect the performance of the page.