Dark theme via DarkReader (#595)

* Initial commit for dark theme.

* Use DarkReader.auto() to watch for system theme.

* Tunning default parameters.

* Allow configurable number of recent posts.

* Added invisible element to hack theme initialization.

* Added default value.

* Use Darkreader CDN.

* Cleanup to keep darkreader in as few files as possible.

* Renamed darkmode.js to darkmode-darkreader.js.

* Bring back the initialization.

* Added provider property.

* Added theme selector to the posts navbar.

* Removed extra line breaks.

* Changed darkreader CDN to local copy.

* Renamed to darkMode.

* Fixed CodeQL failures.

* Added icons.

* Renamed function.

* Added SVG inversion.

* Used icons for selection.

* Toggle initial dark only in the dynamic navbar.

Co-authored-by: donfiguerres <donfiguerres@github.com>
Co-authored-by: Emruz Hossain <hossainemruz@gmail.com>

layouts/partials/navigators/navbar-2.html

@@ -47,6 +47,9 @@
       {{ if .IsTranslated }}
         {{ partial "navigators/lang-selector-2.html" . }}
       {{ end }}
+      {{ if site.Params.darkMode.enable }}
+        {{ partial "navigators/theme-selector.html" . }}
+      {{ end }}
       </ul>
     </div>
   </div>