[frontend] api /project/list to skip group projects
    
    The fact that user historically created the group project
    (copr.user_id == user.id) doesn't necessarily mean that the same
    user can still maintain the project (see PR#780).
    
    So unless owner is explicitly specified to @group, the query
    shouldn't pollute the output by group projects by default.
    
    Also, we only print the "name", not "full_name" -- so it was
    also hard to recognize what project was user-project, and what was
    group-project.