Allow filtering the user's project by access
    
    This commit allows to return only some of the projects the user is
    involved in based on their access level instead of returning them all.
    
    It also replaces SQL based counts of the projects by simple call to
    ``len()`` in python since the SQL query itself isn't paginated.
    
    Fixes https://pagure.io/pagure/issue/2738
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>