Resolve "Add absence management to course book student dialog"

Closes #261

See merge request !360

This is untested since the backend is missing so far!

The latter is not integrated yet.

Query can send no school-term and will receive the result for the
current school-term. With the additional school-term parameter the
frontend now knows which school-term is current.

Not shure if they should be kept insided the main
StatisticsForPersonCard or pushed into the subcomponents.

Previously there was a statistics undefined error while apollo was
still loading.

person & schoolTerm are both objects now in personOverviewCardMixin.