[WIP] Fetch low-level acoustic data from Essentia

[Danoloan10]

The JSON data produced by the Essentia extractor is the same as the one provided by the AB API. We should be able to use Essentia as a library by looking at the extractor example.

[epoupon]

Thanks for this.
For now I am working on #274 (which is actually inotify integration)
As AcousticBrainz states they will shut down their service in early 2023, I will first completely remove the engine in the next release to have time to properly work on restoring it afterwards.