Include 'active' for current sidenav context

This will allow targeted styling of the active element in the side nav

Author: codealchemy

app/helpers/rails_admin/application_helper.rb

@@ -123,6 +123,7 @@ def navigation(parent_groups, nodes, level = 0)
         nav_icon = node.navigation_icon ? %(<i class="#{node.navigation_icon}"></i>).html_safe : ''
         css_classes = ['nav-link']
         css_classes.push("nav-level-#{level}") if level > 0
+        css_classes.push('active') if defined?(@action) && current_action?(@action, model_param)
         li = content_tag :li, data: {model: model_param} do
           link_to nav_icon + node.label_plural, url, class: css_classes.join(' ')
         end