Introduce Dark Mode

This commit mainly changes the color definitions. Mostly, those changes are semantically equally, but there are a few changes that occurred to align the color scheme within the app.

app/assets/javascripts/community_solution.js

@@ -20,6 +20,7 @@ $(document).on('turbolinks:load', function() {
             CodeOceanEditorSubmissions
         )
 
+        $(document).on('theme:change:ace', CodeOceanEditor.handleAceThemeChangeEvent.bind(CodeOceanEditor));
         $('#submit').one('click', CodeOceanEditorSubmissions.submitCode.bind(CodeOceanEditor));
         $('#accept').one('click', CodeOceanEditorSubmissions.submitCode.bind(CodeOceanEditor));
     }