Pages can not be copied by administrators as DataHandler will copy all
pages, including tx_tracking_* tables.
Those are not allowed on tables which will result in error messages.
A test is added to simulate the action and ensure it doesn't fail with
errors.
Results: #52
Allow integrator to limit results in widget to certain languages.
If only one language is allowed, labels will be translated.
Otherwise default system language is used.
E.g. one record will be displayed in multiple languages, it would be
confusing to show him multiple times for each language.
Add TYPO3 extension for phpstan as many things would break within tests.
Relates: #15
