switch to ScatterGL method from Bqplot

[cornhundred]

We will try to switch the location based plotting to ScatterGL which uses WebGL to dynamically visualize lots of scatterplot data points.

• allow pan/zoom
• allow lasso selection
• UMAP
  • RNA-velocity arrows
  • have different embeddings saved (e.g. ADT/GEX based embeddings)
• Overlay tissue image underneath (if possible, may require changes)
• Scatter -> Heatmap communication
  • highlight subset of columns

Based on the examples, it seems like this is not too difficult to set up.