refactor: replace gulp by webpack and npm scripts (#258)

BREAKING CHANGE: We have replaced `gulp` with `webpack` and `npm scripts` to build this theme. If you build it on your own or use build commands during the deployment, you may have to adjust your setup.

BREAKING CHANGE: The `GeekblogIcons` font is using the icon name as Unicode now. As a consequence, you have to replace all references to Icons from this font if you have customized the theme.

BREAKING CHANGE: We have refactored the search integration to split Hugo templates from JavaScript code. To get it working again, you need to adjust the `outputFormats` and `outputs` in your Hugo configuration file, as [documented](https://geekdocs.de/usage/configuration/#site-configuration).

.gitignore

@@ -1,26 +1,21 @@
 # local environments
 .swp
 .env*
-dist/
-build/
-node_modules/
-lhci_reports/
-exampleSite/themes/
-exampleSite/public/
+/dist/
+/build/
+/node_modules/
+/lhci_reports/
+/exampleSite/themes/
+/exampleSite/public/
 CHANGELOG.md
 
 # auto-generated files
-assets/sprites/
-static/*.min.css
-static/*.min.css.map
-static/js/
-static/favicon/
-static/fonts/GeekdocIcons.*
-static/fonts/KaTeX_*
-resources/
-exampleSite/resources/
-exampleSite/data/sprites/
-data/assets.json
+/data/
+/static/
+/assets/sprites/
+/resources/
+/exampleSite/resources/
+/exampleSite/data/sprites/
 
 # testing
 .lighthouseci/