feat(css minimize): add CSS minification in production build for all templates.

[etimesg]

As discussed on #844, this PR allows webpack to compress all CSS using the minimize property from the css-loader plugin. It only applies when --env.prod is provided.

Please note this will also compress any css passed through webpack, therefore you should expect a small reduction in size on files other than vendor.css. Out of curiosity, I'm posting a comparison for each template, showing all the affected files their corresponding sizes before and after this change.

Finally, I also would like to highlight the following passage from the css-loader project:

In some cases the minification is destructive to the css, so you can provide some options to it....

Although I couldn't find any errors while testing the templates, I encourage everyone to read the css-loader documentation in case of a css compression error.

• Angular2Spa Template

  File	css-loader	css-loader?minimize	Diff (%)
  vendor.css	315kB	286kB	29kB (9.21%)
  main-client.js	12.2kB	11.1kB	1.1kB (9.02%)
  main-server.js	150kB	146kB	4kB (2.67%)
  Total	477.2kB	443.1kB	34.1kB (7.15%)

• AureliaSpa Template

  File	css-loader	css-loader?minimize	Diff (%)
  vendor.css	315kB	286kB	29kB (9.21%)
  app.js	26.4kB	26.1kB	0.3kB (1.14%)
  Total	341.4kB	312.1kB	29.3kB (8.58%)

• KnockoutSpa Template

  File	css-loader	css-loader?minimize	Diff (%)
  vendor.css	315kB	286kB	29kB (9.21%)
  0.js	1.17kB	1.12kB	0.05kB (4.27%)
  1.js	2.01kB	1.98kB	0.03kB (1.49%)
  2.js	0.577kB	0.563kB	0.014kB (2.43%)
  main.js	5.99kB	5.90kB	0.9kB (1.5%)
  site.css	1.52kB	0.729kB	0.791kB (52%)
  Total	326.2kB	296.2kB	29.9kB (9.19%)

• ReactReduxSpa Template

  File	css-loader	css-loader?minimize	Diff (%)
  vendor.css	315kB	286kB	29kB (9.21%)
  main-server.js	94.2kB	93kB	1.2kB (1.27%)
  site.css	1.52kB	0.729kB	0.791kB (52%)
  Total	410.7kB	379.7kB	30.9kB (7.55%)

• ReactSpa Template

  File	css-loader	css-loader?minimize	Diff (%)
  vendor.css	315kB	286kB	29kB (9.21%)
  site.css	1.52kB	0.729kB	0.791kB (52%)
  Total	316.5kB	286.7kB	29.7kB (9.41%)

• VueSpa Template

  File	css-loader	css-loader?minimize	Diff (%)
  vendor.css	315kB	286kB	29kB (9.21%)
  main.js	21.8kB	21.6kB	0.2kB (0.9%)
  Total	336.8kB	307.6kB	29.2kB (8.67%)

Please, feel free to recommend/perform any necessary modifications.

[dnfclas]

@etimesg,
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[dnfclas]

@etimesg, thanks for signing the contribution license agreement. We will now validate the agreement and then the pull request.

Thanks, .NET Foundation Pull Request Bot

[SteveSandersonMS]

Thanks very much for this! I really appreciate your thoroughness in providing all the stats on the difference this makes.

Just a few minor tweaks and we can get this merged :)

[SteveSandersonMS]

In a few cases you've added spaces inside the [...] array, such as in this file, but not in some other cases (e.g., for ReactSpa's webpack.config.js).

Would you be able to make the changes consistent with each other? Personally I'd prefer not having the extra spaces in any of them, but if you prefer them to be there, that's OK as long as they are all the same :) Thanks!

[SteveSandersonMS]

Actually don't worry about this. It's a super-minor issue. I'll make a follow-up tweak to the spacing later.

[etimesg]

Thank you @SteveSanderson. In truthiness, the differences in spaces also bothered me, until I realized other parts of the templates were different, so I decide to keep it as it was. But now that I'm aware of your preferences for this project I'll make sure to use "no array spaces" as the standard on future PRs.

[SteveSandersonMS]

Looks great - thanks! I really appreciate seeing all the stats on the difference it makes :)

[SteveSandersonMS]

@etimesg In case you got a notification with some other review comments from me, you can ignore it, because I realised my comments were wrong so I deleted them.