list limits for documentslist
garbage collection: 3 types:
  generic/common (generic tables, affects all apps)
  generic/per-app (generic tables, per application)
  <app> (application-tables; effect is application dependend)
sql_prune_logbook(): support $prune_level
rename: programme_id -> programme_flags (is not a primary key, avoid misinterpretation)
repair logbook view
remove redundante column fron table logbook