Remove cards and popovers for now

The concept was not thought through well, and we should redesign it after migrating to materialize and all the related things we might get during the SchoolApps merge.

changed due date to January 01, 2020

added part::frontend label

(In all apps)

created merge request !80 (merged) to address this issue

mentioned in merge request !80 (merged)

closed via merge request !80 (merged)

mentioned in commit 3b53e767