Avoid using QApplication in core.
Drop entries from search results when moved to the recycle bin.
Allow removing multiple entries.
Add a QMessageBox wrapper class to help gui tests.

QMessageBox displays modal dialogs which blocks the gui tests.
To work around this we add a MessageBox wrapper class where
the tests can set the answer for the next dialog.
The answer is then returned without actually showing the dialog.
Add tests for the multi-entry delete feature.
Test that the delete action moves entries to the recycle bin.
Add gui tests for deleting entries from the recycle bin.
Make use of the TestGui::clickIndex() helper function.
Avoid modulo bias in Random::randomUInt().
Support custom backends in Random.

Useful for tests.
Add tests for Random::randomUInt() and randomUIntRange().