Change icons of features on admin dashboard to remove bias (#10366)

Red crosses implied that it was bad/unexpected that certain features
were not enabled. In reality, they are options, so showing a green
or grey power-off icon is more appropriate.

Add status of timeline preview as well

Fix sample accounts changing too frequently due to wrong query

Sample accounts are intended to be sorted by popularity

app/helpers/admin/dashboard_helper.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module Admin::DashboardHelper
+  def feature_hint(feature, enabled)
+    indicator   = safe_join([enabled ? t('simple_form.yes') : t('simple_form.no'), fa_icon('power-off fw')], ' ')
+    class_names = enabled ? 'pull-right positive-hint' : 'pull-right neutral-hint'
+
+    safe_join([feature, content_tag(:span, indicator, class: class_names)])
+  end
+end