Graph/scatterplot improvements

[bkmartinjr]

This PR includes a number of enhancements and refactors of both the main graph and scatterplot widgets:

• graph pan now is synchronized with mouse movement. Fixes main embedding pan does not have 1:1 drag with cursor #722
• graph zoom centered on mouse location. Fixes center zoom on mouse location #758
• graph RAF no longer runs infinite loop, which will save battery/CPU. Fixes RAF loop always active in graph pan/zoom mode #882
• significant cleanup/refactoring of both graph and scatterplot rendering. In particular, both move to a 2D model, using a set of simple 2D transforms to control camera & projection. Fixes scatterplot needs refactoring/cleanup #886
• for both plots, points now stack: highlighted on top, NaNs/clipped on bottom, all else in middle.
• for both plots, NaN/clipped data will be alpha 0.9, all else 1, improving visibility of non-NaN data.
• a large number of (now) unnecessary JS module dependencies removed (eg, the 3D orbit-camera)

Still to come as future PRs built on top of this, but not included in this PR:

• dot rendering improvements, including Scaling the dot size based on number of points #759, etc.
• showing hover-over state in scatterplot, scatterplot does not show categorical highlighting state #892
• constraining pan so you can't pan all of the graph off-canvas

[liaprins-czi]

This all looks good to me!

[liaprins-czi]

Checked out the branch, and all of the UI-related changes look great!