simplify roles organization and renames

roles/mediaserver/meta/main.yml

roles/mediaserver/tasks/main.yml

roles/mediaserver/templates/celerity-config.py.j2

roles/mediavault/defaults/main.yml

roles/mediavault/handlers/main.yml

roles/mediavault/meta/main.yml

roles/mediavault/tasks/main.yml

roles/mediavault/templates/systemd-backup-service.j2

roles/mediavault/templates/systemd-backup-timer.j2

roles/mediavault/templates/systemd-mailer-script.j2

roles/mediavault/templates/systemd-mailer-service.j2

roles/mediaworker/defaults/main.yml

roles/mediaworker/handlers/main.yml

roles/mediaworker/meta/main.yml

roles/mediaworker/tasks/main.yml

roles/mediaworker/templates/celerity-config.py.j2

roles/mirismanager/files/set_site_url.py

roles/mirismanager/handlers/main.yml

roles/mirismanager/meta/main.yml

roles/mirismanager/tasks/main.yml