Track and store failed app metadata extracts

[mountaindude]

In the best of worlds metadata for all apps will be extracted by Butler Spyglass.
But if som apps for some reason fail to extract, this should be recorded to disk so it is clear what went well and what failed.

[mountaindude]

Even better, store the failed app extracts to a separate retry queue, which can then run in parallel with (or after) the regular app extract queue.