Migrate to rollup from webpack

[saschanaz]

#2553 needs compiling some dependencies (specifically marked and pluralize) to es modules instead of previous copydeps so that es module system can load them. Webpack does not support emitting es modules yet (webpack/webpack#2933), maybe we should migrate to rollup to do this.

(Currently #2553 uses forked ES module versions of those dependencies, but maintaining forks is a burden.)

[marcoscaceres]

I don't mind, so long as we get a development server and don't need to (re)compile the code test it.

[saschanaz]

Compiling dependencies would happen after npm install as current copydeps do, so it shouldn't make additional burden when testing 👍

[saschanaz]

Closed by #2553