fix: Remove hash routing on GitHub pages

[ShrimpCryptid]

Closes #213, removing hash routing on GitHub pages. This means we don't need to include the # character for subpaths anymore, so our S3 and GitHub Pages will use consistent link formats.

Before: https://allen-cell-animated.github.io/website-3d-cell-viewer/#/viewer After: https://allen-cell-animated.github.io/website-3d-cell-viewer/viewer

Estimated size: medium, 20-25 minutes

Changes

This uses a custom 404 HTML page catch missing pages and reroute the browser to the viewer's base index.html page. The base page checks for the redirect and, if found, redirects internally to the correct page.

See https://github.com/rafgraph/spa-github-pages for the original solution.

• Adds route_utils.tsx for handling routing of URLs, and associated unit tests.
• Adds a custom reroute.tsx and 404.html page to reroute missed traffic to the root single-page-app.
• Updates index.tsx to intercept the redirects and route the client to the correct page.
• Updates the GitHub actions for deploying to GitHub Pages and S3 to add missing basename information.
• Configures webpack to handle multiple entrypoints.

Testing:

(this link will break after today so ping me if you want to see it again)

• Open https://allen-cell-animated.github.io/website-3d-cell-viewer/viewer. The viewer should reroute to our custom viewer.

[ShrimpCryptid]

The functions that do the url manipulation look complicated and unreadable enough to merit unit tests but that could be for a future ticket.

yeah... I could move this into index.tsx and the functions into their own typescript files.

[ShrimpCryptid]

Taking this back to draft while I do some reworking!

[ShrimpCryptid]

@toloudis re-requesting your review because I've made some substantial changes. The reroute code now lives in a typescript file with unit tests, and I added more styling to the 404 page (as well as some webpack config changes).