Update UMD builds (#161)

* Add additional Rollup plugins

* Rework UMD build process to fix multiple issues

- Added replace of "process" usage in dev build to fix crashes
- Added minified production UMD build
- Restructured conditional import of immutable middleware so that
  each build works correctly:
  - CJS/ESM: use conditional require in dev/prod, with shaking
  - UMD Dev: use import statement to pull in middleware
  - UMD Prod: drop middleware completely

Author: markerikson