Scroll dropdowns.

misago/static/misago/css/misago/dropdowns.less

@@ -10,6 +10,9 @@
   box-shadow: 0px 0px 0px 6px @dropdown-shadow;
   margin-top: 12px;
 
+  max-height: 310px;
+  overflow-y: auto;
+
   &:after {
     border: solid transparent;
     border-bottom-color: @dropdown-bg;