cockpit: Stop importing cockpit's base1/patternfly.css

This is deprecated API and will be dropped at some point, in favor
of projects shipping their own CSS.

Follow https://github.com/cockpit-project/starter-kit/blob/master/webpack.config.js
approach on how to use PF CSS.

Also:
* Replace extract-text-webpack-plugin with mini-css-webpack-plugin as
the former is deprecated: https://webpack.js.org/plugins/extract-text-webpack-plugin/#usage
* Upgrade PF module dependency
* Reduce the css files that are linked through webpack. Instead include
from the JS the CSS files and let mini-css-extract-plugin do the rest of
the work

lib/patternfly/patternfly-4-cockpit.scss

@@ -0,0 +1,15 @@
+/*
+ * Keep in sync with https://github.com/cockpit-project/cockpit/tree/master/src/base1/patternfly-4-cockpit.scss
+ */
+
+/* Set fake font and icon path variables - we are going to indentify these through
+ * patternfly.sed and remove the relevant font-face declarations
+ */
+$pf-global--font-path: 'patternfly-fonts-fake-path';
+$pf-global--fonticon-path: 'patternfly-icons-fake-path';
+$pf-global--disable-fontawesome: true !default; // Disable Font Awesome 5 Free
+
+@import '~@patternfly/patternfly/patternfly-base.scss';
+
+/* Import our own fonts since the PF4 font-face rules are filtered out with patternfly.sed */
+@import "./fonts";