• reworked the ways of handling relations of feed and episodes, and of queue and episodes
  • may cause issues due to possible incomplete migrations!
• in Queues screen, systematic sorting is performed only when requested, allowing manual sorting as long as queue is unlocked
• introduced type Volume that can contain sub-volumes or feeds, all volumes have a nullable parent volume
• all feeds have a parent volume (by default null)
• in Subscriptions, show top volumes (if any) at the top of the list, and feeds whose parent volume is null
  • from menu, a volume can be created
  • when a volume is clicked, sub-volumes and/or feeds belonging to the volume are shown
  • long-press a volume shows prompt to delete the volume
    • deleting a volume will delete all sub-volumes and feeds under it (local files stay intact)
  • in feeds multi-select menu, selected feeds can to set to a parent volume
• in Feed Settings, added setting of parent volume
• allows adding local directory tree, from "drawer->Add podcast->Advanced->Add local folder"
  • directory is traversed indefinitely
  • if a directory has only sub-directories, it's added as a volume
  • otherwise, it's added as a local feed
• fixed various issues of playing local media
• fixed updating local feeds requiring network
• fixed download failure due to DB write transactions
• in LocalMediaPlayer, added audio offload listener with toasts on whether audio is offloaded
• enhanced colors on multi-select popup menus
• some code refactoring