Add an option for preventing file deletion on media translation

Problem/Motivation

Deleting file entities referenced by a media translation might not always be desired. Other translations are left without any reference to a file. It should be possible to control whether to show the file deletion option while deleting media translations.

Steps to reproduce

Proposed resolution

Add configuration option which makes it possible to disallow deleting a file referenced by a translation. Enabling the option will make the deletion toggle visible only on the translation source media.

Remaining tasks

Implementing the feature.

User interface changes

API changes

Data model changes