Implement Vue substitution frontend

When a user has the required permission(*), lessons in the timetable should have a "manage" or "substituion" or something like that, button. Clicking on it should open a dialog (?), in which subject, teachers and room can be altered and an option to mark the lesson as cancelled and to write a comment are provided.

*: See rules.py in Chronos. There are things like chronos.edit_substitution_rule that can be used and (if necessary) be adjusted.