Show a preview of the project competencies for entries

[tomhaerter]

When adding a project to an entry, it should be shown which competencies are documented by the project.

This is important because otherwise the creator may think that the project competencies are not working properly and may try to add the competencies manually.

It should also be considered that instead of just referencing the project competencies, a copy of the current project competencies is created and stored, e.g. as entry_project_competences with a project_competence_reference_id: nullable.