Persist open playlists in configuration file

[Borewit]

Store open playlist-editors in configuration file options.json on exit and reloads the playlists (at least those which still exist).

Resolves #70

[Borewit]

Build: listFix_2.6.0-PR141-34.exe

[Borewit]

Original sequence of tabs is not preserved, I will change that.

[touwys]

Testing: listFix_2.6.0-PR141-34

Original sequence of tabs is not preserved, I will change that.

Thank you, I noted that, and I herewith confirm this positional change of the restored tabs, does occur.

✔️ During testing, I loaded many different playlist combinations, and every one of them closed and opened efficiently upon restart — except for the aforesaid incorrect tab sequence. So I guess it's safe to move onto the next stage of your plan, once the sequence issue is sorted out.

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ℹ️ The dragging and dropping of playlists into the Editor work really well. During the current test, however, I discovered that something is amiss — support for the dragging and dropping of playlists from the Playlist Directory directly into the Playlist Editor. I propose that you consider adding it, in order to fulfil the drag-and-drop function.

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[touwys]

Original sequence of tabs is not preserved, I will change that.

@Borewit : Did you also catch that not only are the tabs getting restored out of sequence, the tab that was busy getting edited upon exiting, is not getting restored as the active one?