Resolve "Appointment with 0 length can be added (question)"
Closes #464 (closed), #462 (closed), #434 (closed)
The warning is added. Moreover, there are few cascading issues with the model. Here is a list of cascading issue that could be triggered by user but should not:
| Object Type | Affected object | New behaviour |
|---|---|---|
| Flying team | Appointment | FORBIDDEN |
| Room | Appointment | FORBIDDEN |
| Location | Appointment | FORBIDDEN |
| Language | Subject (Default language for document generation) | SET NULL |
Edited by Piotr Gawron