Improve display of image data

[dylanmcreynolds]

Currently images are displayed as grey scale, with no features for zooming. This done by transforming the image to jpeg and string encoding it on the server.

I'd like to improve this. With the MLExchange apps, we use Plotly Dash, which itself uses Plotly.js...so using Plotly.js in SPAs would probably result in a similar experience. This would also easily support colormaps.

If we sent raw array data to the browser, we might also want to consider downsampling the images. But I'd hold off until seeing what the performance is like.

Tagging @Wiebke and @davramov in case they have opinions on this.

[SeijDeLeon]

#23 -Initial change to plotly heatmap display
#24 -Further refinements to heatmap scaling and user controls

Images are now displayed in plotly heatmap with Viridus color scale.