Show parallel lessons in timetable management view on drag of lessons

The following discussion from !2 (merged) should be addressed:

• @ZugBahnHof started a discussion:

  We want to display two notes in the timetable management view when a lesson is dragged: a note for every lesson the room is used a note for every lesson the teacher has a lesson

  This can be done by simply loading the plan of the room and the teacher