#1 Bad model indices while modifying data

[Marcel Taeumel]

There is a problem with deleting an entry. You can take an item from the model but neven delete it! If you do so, the app crashes.

Due to unit testing I found out that several (sometimes invalid) model indices have internal pointers to these data structures.

We should try to find out, how we can delete an item of the data tree to avoid memory leakage. Maybe suspicous model indices have to be determined for that.