Upgrade picoModal to 2.0.1

This is the latest upstream version, available at this URL:

  https://github.com/Nycto/PicoModal/releases/tag/2.0.1
Switch to the non-minified version of picoModal to ease debugging

The addon will be gzipped anyways, so the size difference should
not matter too much (3.4k v. 1.4k).