Resolve "Use icons instead of plain text"

Closes #80

See merge request BiscuIT/BiscuIT-ng!73

Resolve "Migrate to material-design-icons"

Closes #116

See merge request BiscuIT/BiscuIT-ng!67

This reverts commit ce766c73.

 * Update django-two-factor-auth to current release
 * Allow phunnumber-field 3.x or 4.x while django-two-factor-auth
   still crunch https://github.com/Bouke/django-two-factor-auth/pull/326
 * Run poetry update
   * Update django-image-cropping and easy_thumbnails for DJango 3.0 support
     (cf. !61 and #75)

Closes #117.