[Lesson substitution] View with all lesson substitutions in the future

We need a view that simply lists all known lesson substitutions in the current week and the next week.

changed milestone to %1.0a1

added part::frontend prio::2 type::feature labels

mentioned in commit e5980467

mentioned in commit c995a868

mentioned in commit 068d3452

mentioned in commit b83c6f86

changed milestone to %1.0a3

mentioned in merge request !21 (merged)

created merge request !21 (merged) to address this issue

closed via merge request !21 (merged)

mentioned in commit 3039a61f