Playlist folder support

[DennisvHest]

• Show folders in playlist lists
• Move playlist in folders
• Delete/rename folder (?)

TODO:

• [x] Add expand/collapse all
• [x] Fix selected playlist no longer being shown selected after renaming parent folder (not fixing)
• [x] When playlist folder is edited, the playlist should be moved to the selected folder
• [x] Add filter to select only regular playlists or dynamic playlists
• [x] Add icon or something to dynamic playlists in list to be able to distinguish
• [x] Update playlist selector popup (reuse component?)
• [x] Searching on folder name?
• [x] Fix nullrefs from Pather.CSharp when arranging dynamic playlists
• [x] Fix generated playlist cover on create or edit of playlist maps
• [ ] Add tooltip to playlist name in play list list

[DennisvHest]

If there are 2 playlists with the same name, but in different folders, one of the playlists cannot be selected:

After a complete reload, it looks like both of the playlists have the same maps, but this is not the case when looking in the playlist files.