Mobile-friendly layout

[normanrz]

Detailed Description

A low-hanging fruit to make Webknossos more mobile-friendly is to collapse the sidebars on mobile browsers by default. That increases the viewport of the data and makes it possible to scroll around.
We should think about how to detect mobile browsers.

Context

While it is not useful to do serious work in wk on a phone, it can be useful to showcase some data. The ability to scroll around a bit would be nice.