add bottom-up styles to the dropdown menus

lib/dropdowns.less

@@ -54,6 +54,13 @@
   *border-right-width: 2px;
   *border-bottom-width: 2px;
 
+  // Allow for dropdowns to go bottom up (aka, dropup-menu)
+  &.bottom-up {
+    top: auto;
+    bottom: 100%;
+    margin-bottom: 2px;
+  }
+
   // Dividers (basically an hr) within the dropdown
   .divider {
     height: 1px;