Keep referenced entities

Provides protecting some entities from deletion if they are used in other entities.

For example, I have entity Student which has reference to entity School.
I can delete Student because School will be School without this Student.
But If I'll delete School, Student cannot be Student.

So, the School should be protected. And this module allows doing this.

Features:

• Protect entity from manual deletion
• Protect entity from programatic deletion
• Choosing types and bundles of entities which should be protected from deletion

TODO:

• Add an option "Protect all"
• Support handling of references through views
• Add hook to implement custom reaction of deletion of entities programmatically
• Add custom theme function for information about referenced entities on "confirm deletion" form