Deprecate modernizr

[thet]

Our standard Patternslib bundles include the feature-detection module, which loads the "Modernizr" library.

Nowadays this is not necessary anymore. Modern browsers already include a lot of feature detection code via CSS at-rules. Also the JavaScript detection via the js class is not necessary aynmore - this can be done with the scripting at-rule.

Also @emmanuelkaufmann already works on CSS code which does not depend on Modernizr anymore.

If we make the Modernizr library optional, we avoid to load the minified 30kB modernizr library and spare a lot of feature detection tests, which are unnecessary these times.

See:

• https://github.com/Patternslib/Patterns/blob/master/src/core/feature-detection.md
• https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@media/scripting
• https://caniuse.com/mdn-css_at-rules_media_scripting