Export-import report between projects with different namespaces - uncaught exception

[konyashkina]

Related to #285.

CUBA Platform version: 7.2-SNAPSHOT
CUBA Studio plugin version: 15.4-202
IntelliJ version: IntelliJ IDEA 2021.1.3 (Community Edition)

Steps:

1. Create a new CUBA project and set some project namespace.
2. Add Reporting add-on.
3. Run application.
4. Create new report group with title "report".
5. Create new report and set group = the new group "report".
6. Export created report (Report exported successfully to zip file).
7. Create a new project with different project namespace. Add Reporting add-on to the new project.
8. Run application.
9. Create new report group with title "report".
10. Try to import report from the zip file.

ER: Correct message about namespaces mismatching.

AR: Red error message.