Redesign contact list

Inspiration by the GNOME Project:

Source: https://gitlab.gnome.org/Teams/Design/os-mockups/-/blob/f69fa82f8676582d900af8716522a27ddd77d87f/mobile-shell/mobile-shell-convergence.png

added UI/UX label

added Design Good first issue Help wanted labels

mentioned in issue #80

marked this issue as related to #80

This should be done after #80 imho and therefore it's S: blocked for now.

added S: blocked label

mentioned in issue briar-desktop#262