Remove artefact from project

Allow users to remove artefacts from a project according to the following rules:

* Users cannot remove artefacts from projects;
* Admin users can remove artefacts from any project.

It is mandatory to create a project log every time an artefact is removed from a project.

The issue names no files, tests, or entry points. Start by locating the project and artefact management code, then trace authorization for removal and the existing project-log mechanism. Done means enforcing the user and admin rules and creating a project log for every successful artefact removal.

Written by the indexing model from the issue text.