Make sidebar fully responsive

[SilvanVerhoeven]

Currently, the ToC is responsive and is moved into a drawer on mobile. To not force mobile users to scroll over the whole content to the bottom, the attachments are located there, too.

This may not be expected. Also, further meta information like "last edited" and "meeting participants" are still at the very bottom.

Find a good way to better incorporate those information and attachments. Some ideas:

1. Add second button below the toc button to open a sidebar with that information
2. Add a jump to bottom button

[SilvanVerhoeven]

@jeriox Any input on how to do this properly?