Add native Essentia functionality

[Supinic]

Instead of relying on various binaries randomly strewn around users' operating systems, use the Essentia module directly. Probably as a new functionality, so that using a direct path to the beat-mapping executable is still available as a fallback.

[Supinic]

Essentia.js docs

[Supinic]

So far, seems like essentia.js is directly linked to being run in a browser - e.g. depending on fetch existing as a global, and depending on AudioContext being passed in order to create an audio signal vector.

There is discussion about getting a proper Node.js example in the repository, but unfortunately, it doesn't seem like this is possible at the very moment.

Further updates here: MTG/essentia.js#44

[Supinic]

Sample implementation