Notifications show changes although nothing has changed

[d-Rickyy-b]

This needs to be fixed asap

[d-Rickyy-b]

This is a bug because of the class K2 can have multiple cancellations of the same subject (e.g. history) which take place in different rooms.

For example:

3-4 | Geschichte | --- | H105 | --- |  
3-4 | Geschichte | --- | H202 | --- |