Port clustering feature to new UI and deploy

[ffont]

The search results clustering feature has been half-implemented for ages and it is time to port it to the new UI, run some tests and finally deploy it. This requires some things to be done in the search page, so it might be good to take this opportunity to also do some refactoring of the search page so it becomes easier in the future to add/remove search features.

[ffont]

In PR #1756 we do arefactor of the search page and implement a basic porting of the clustering feature to the new UI. The clustering feature is only available as a "beta" search feature. We should run some analysis to estimate the impact of deploying such feature to the general public and we should also design a better UI for the representation of clusters as right now we simply show some selection of tags for the sounds inside a cluster. This could be improved by, e.g., showing some spectrograms of example sounds from the cluster and even being able to play them on mouse hover or something like that?