pref-filters: add a button to hide or show rules in the filter list

themes/compact.css

@@ -1728,6 +1728,9 @@ body.ttrss_utility fieldset > label.checkbox {
   display: inline;
   font-weight: normal;
 }
+body.ttrss_prefs[hide-filter-rules="true"] ul.filterRules {
+  display: none;
+}
 body.ttrss_utility.sanity_failed {
   background: #900;
 }