Cluster widget puts results in properties

[jo-mueller]

I just realized that while the dimensionality reduction widgets puts its results (e.g., UMAP0andUMAP1) in the features table, but for the cluster widget this somehow ends up in layer.properties- where the plotter doesn't find it if there is already stuff in thefeatures`.

[zoccoler]

This seems the place where new columns are set. It should add it in both properties and features.