Use timezone aware datetime objects for pseudo hades log entries
Use timezone aware datetime objects for pseudo hades log entries

`datetime.today()` is misleadingly named alias of `datetime.now()` that
should be avoided. Additionally it does not support timezone aware
datetime objects.

Refs #200

agdsn/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft