Clean up minified and non-minified sources for wtb

[camillobruni]

• Add webpack config for generating non-minified sources
• Add build-prod and build-dev scrip
• compress js.map files
• Globally use webpack --progress for better building

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[danleh]

Minor nit: typo in the commit/PR title (wbt -> wtb)
Quick questions (I don't really know these JS line items very well):

• Why do we have these new web-tooling-benchmark/dist/*.LICENSE.txt files? Were the sources updated as well, besides the build scripts?
• IIUC, the .map.z files are source maps to map minified JS code back to the original ones, but only the minified ones are checked into the repo, right? In that case, should we remove .map.z files from the repo as well?