v5 update

[benkeen]

I'm in the midst of updating the architecture for this application, so please note master will be in a broken state until it's completed.

Notes on the changes here:
https://github.com/benkeen/generatedata/blob/master/V5_CHANGES.md

[benkeen]

Remaining work:

• initial preview render shows undefined
• full code review
• panel layout incorrect onload after saving, then loading in a fresh browser window with different dimensions.
• update to new react-split-pane when available
• blank page when first starting webpack-dev-server
• DOCUMENTATION!
• webpack config needs to imports from @generatedata/config, meaning ESM or adding CJS exports for that package
• remaining dependabot issues