[W.I.P.][Migration] Webpack 4 - detecting outstanding issues.

[DorianGrey]

Just tested... and there still are tons of errors due to incompatible loader resp. plugin versions. But it seems I'm not the only one facing these ... Below are the errors I was able to figure out shortly, in addition to a couple of PRs containing (potential?) fixes.

• resolve-url-loader: Webpack 4: Cannot read property 'resolveUrlLoader' of undefined bholloway/resolve-url-loader#79 (had to disable the corresponding config block to further check things). Pending PR: Possible fix for #79 bholloway/resolve-url-loader#80
• stylelint-webpack-plugin: Webpack v4 Support webpack-contrib/stylelint-webpack-plugin#137 (removed it from config temporarily for further checking). Pending PR: Add webpack4 support; webpack-contrib/stylelint-webpack-plugin#140 Done.
• autodll-webpack-plugin: Webpack 4 support asfktz/autodll-webpack-plugin#105 Already has a PR pending - [WIP]: webpack 4 support asfktz/autodll-webpack-plugin#106. Is optional to wait for, since we might move back to manually generate them.
• extract-text-webpack-plugin: Webpack 4 compatibility webpack-contrib/extract-text-webpack-plugin#701. Addressed in refactor(plugin): v4.0.0 webpack-contrib/extract-text-webpack-plugin#685. Will never support webpack 4, thus it has to be replaced with https://github.com/webpack-contrib/mini-css-extract-plugin. However, this will require vue-loader v15 to get rid of the immediate dependency to ETWP. Done with release v15 of vue-loader and migration to mini-css-extract-plugin.

Other problems detected:

• Need to provide a polyfill for Array.prototype.includes to support IE11 during development (refactoring placed in Refactor/indexof to includes webpack/webpack#6298) - yeah, nobody likes this browser, but it's still a requirement in quite a lot of use-cases resp. projects, thus ...
• Some styles of vue-carousel-3d somehow get lost. Neither the purge nor the optimize CSS plugin are responsible for this. Seems to have something to do with the way styles of lazy-loaded component are extracted and picked up. Might have something to do with https://github.com/vuejs/vue-loader. Done, at least mostly. Was a problem with a wrong configuration for CSS extraction. However, it now extracts CSS from chunks that should not have any (runtime and vendor). That's really weird...
• Workbox v3 seems to attempt to import every available module, even though only two of them are in use. That's especially a problem with the google-analytics module, which may get blocked by clients, breaking the whole service worker and thus making it non-functional at all ...

Further changes:

• Removed inline-chunk-manifest-html-webpack-plugin - it's not compatible with webpack 4 atm., and I don't think it is required any longer.

[DorianGrey]

This one was pre-merged, since further updates depend on it.