React/regl client app for displaying point-in-polygon point clouds.

[thomcom]

This app will display 2d point clouds that are returned from an api-server I/O routine.

The app will display a background image that scales and translates with the GL view, displaying points that are contained within the viewport and culling the rest.

Part of the demo will provide an option to disable view translation but retain the viewport culling, so that points are culled from the center of the display, demonstrating the culling.

Depends on #427

Steps remaining:

• Clean up into 2-3 PRs
• Add mouseEvents for translation and scale
• Aim camera at "window center" and rescale points based on window size
• Bind translation and scale to GL view
• Bind translation and scale to background texture
• Load a background image into a regl buffer for the texture
• Add a large datasource to api-server
• Add an api-server endpoint to feed data via arrow
• Load points buffer in app via arrow
• Rearrange coordinate systems

I am going to split this PR up into one for the api-server updates and one for the particles app. There are also updates to sigma.js that need to be pushed to their own PR.

[trxcllnt]

should remove this file before merging

[trxcllnt]

Should remove the file at modules/demo/particles/src/logo.svg too.