Example project for spot sources

[constantinpape]

Hey @tischi,
here is the example project for data with a spot source. For now, I have put it in the dataset pos42-spatial-transcriptomics, because @tibuch is using the default dataset pos42 for implementing mobie/mobie-viewer-fiji#791.

As discussed, we have a spotSource now, that only contains tableData, and where the corresponding default table MUST have columns spot_id, x, y and z. And there is a spotDisplay to add this to a view. For now I have kept the display very minimal, see https://github.com/mobie/spatial-transcriptomics-example-project/blob/main/data/pos42-spatial-transcriptomics/dataset.json for details; and haven't added a lut or anything. You could just color with glasbey based on spot_id in the beginning and we can expand this once loading the spot data is working.