Show precomputed clusters

[vrodriguezf]

Right now, the only way of showing clusters in the visualization app is to click on the button "calculate and show clusters", which is what it is done in the original Timecluster paper. HOwever, in order to integrate some of the works of our colleagues in Poland, it would be interesting to add the possibility to get the clusters from a logged artifact.

The artifact would be a ReferenceArtifact logged by the dr_run, just like it is done with the embeddings, and it could be as simple as an array of cluster labels.

[vrodriguezf]

I think this is already done!