WIP: Improve playlist handling

[sghpjuikit]

Add m3u/m3u8 playlist reading/writing support

• supports m3u & m3u8
• supports relative files
• supports both file & URI
• supports playlists in playlists
  • port PlaylistView to Kotlin
  • add actions/drag&drop to import/export playlist
  • fix recompiling PlaylistView deletes playlist

Remaining problems:

• PlaylistReader may need to be an object, not bunch of util methods
• question remains whether playlist reading/writing should be extensible & whether more formats are desirable. I believe for now this is about ideal. Later there would be generic playlist reader/writer with pluggable readers/writers and capable to generate functionality like export to menus or actions
• because configuration framework does not support obscure Vo properties (overridable properties), currently this functionality in PlaylistView is reduced (it is a non issue, but remains as to be done)