Add initial webpack config

[kristoforsalmin]

So here's the initial webpack config. It's still missing a lot of things, but for now following needs from #54 were addressed:

• gulp replaced with webpack
• Multiple configs via webpack-merge
• Multiple Browserslist environments (modern and legacy browsers)
• assets-manifest.json is being generated
• .env is loaded via dotenv (there's also cross-env for Browserslist)
• core-js updated
• node-sass replaced with sass

@mi2oon I'm keeping to our present structure with Yeoman for the time being.

That's it so far 🙂 Let me know what you think

[sme12]

Split code for modern and legacy browsers is a great thing but it adds some inconveniences to the developing process:

1. The decision which bundle to use should be made on the backend, probably by checking the user agent. I'm not sure if each project is ready to implement this extra logic. And I guess we currently don't have a solution from the box.
2. If we use legacy polyfilled code by default during the development, we need to check the modern code as well in order to make sure it works the same way. That's kinda extra work :)
3. Polyfilled files are outputting to the folder named legacy, which is a common way to name bundle for old browsers, but also might be confused with "legacy" code in the project if it has some :)

Probably we'd better make a code-splitting optional if it is possible, what do you think? :)

[kristoforsalmin]

@sme12 yeah, I also been thinking whether we need to have this sort of setup by default...

1. There's also this <script nomodule> approach. It requires a bit of JS for browsers that don't understand nomodule attribute. Frankly, I need to revisit this topic to see if it makes more sense.
2. That's true. Even though one could argue that you mostly do development in your favorite browser and then still have to test in, say, IE afterwards. But yes, it adds up this extra step of npm run build. In a traditional setup you can go away with the results yielded by already running npm start.
3. legacy/modern words in context of bundling are somewhat common, for example here and here, so I just excused myself from another naming task 😁 However, I see your concern, among other reasonable choices I found were classic/module as seen here (although they convey a slightly different meaning compared to the current solution) and simply old/new (I also like that both words have equal number of characters 🙂).

[kristoforsalmin]

@mi2oon @sme12 I'm going to merge this one, so it isn't up in the air for too long. Let's continue our conversation about the code splitting in #54 😉

[mi2oon]

Looking good.. lets keep the ball rolling 🐤