Make user list responsive

[slauriere]

On small devices, the user list columns become very narrow, displaying them as rows would be best, like what happens with livetables.

See also: https://css-tricks.com/responsive-data-tables/

[raphj]

Here's what I have.

The difference with live tables and with the linked article on responsive tables is that the userList macro does not produce table headers. Which could be an option by the way.