Saving new project with title of existing project leads to error that is only logged in background

[solth]

Describe the bug When a new project is created and the name/title of an existing project is entered before saving, the project is not saved proberly. That is correct behaviour, because projects should have unique titles. Instead, the following error message appears in the logs:

These unhandled FacesMessages are: 
- Es ist ein Fehler aufgetreten: Der Projekttitel wird bereits verwendet.

To Reproduce Steps to reproduce the behavior:

1. Go to "Projects" list
2. Click "New" button and then "Project" button
3. Enter the name of an already existing project
4. Click "Save"
5. Nothing happens
6. Check log

Expected behavior Instead of hiding the error message in the logs, a message in the GUI should inform the user that the project title is already in use.

Release 3.7, current master