Make permission check for coursebook route faster

by not filtering for lesson events & documentations the user fulfils the requirements for viewing them for

instead, think of some better heuristics for determining access

added part::backend label

assigned to @yuha

created branch 318-make-permission-check-for-coursebook-route-faster to address this issue

mentioned in merge request !428 (merged)

mentioned in commit 3c6c0651

closed with merge request !428 (merged)