Make visualization interactive

[carschno]

The JScatter implementation (#33) lies the basis for making more interactive visualizations.

We should use selection by mouse or by metadata (e.g. clusters) to further interact with the data, for instance:

• trigger (further) clustering
• add nearest neighbours from the database
• update clusters manually, e.g. split or merge based on selection

Potentially, multiple linked plots can be used to zoom in and out on selections, clusters, metadata sets etc.