Fix #564

Tentatively adding support for images.

Adding an attribute `data-image-src` to the option element with the
image source url will pull that image into the menu next to that check
box.

jquery.multiselect.css

@@ -15,6 +15,7 @@
 .ui-multiselect-checkboxes { overflow-y:auto; position:relative; }
 .ui-multiselect-checkboxes label { border:1px solid transparent; cursor:default; display:block; padding:3px 1px; }
 .ui-multiselect-checkboxes label input { position:relative; top:1px }
+.ui-multiselect-checkboxes label img { height: 30px; vertical-align: middle; padding-right: 3px;}
 .ui-multiselect-checkboxes li { clear:both; font-size:0.9em; list-style: none; padding-right:3px; }
 .ui-multiselect-checkboxes .ui-multiselect-optgroup { padding: 3px; }
 .ui-multiselect-columns { display: inline-block; vertical-align: top; }

src/jquery.multiselect.js

@@ -194,7 +194,11 @@
         "aria-disabled": isDisabled ? "true" : null
       }).data($(option).data()).appendTo($label);
 
-      $("<span/>").text($(option).text()).appendTo($label);
+      var $span = $("<span/>").text($(option).text());
+      if($input.data("image-src")) {
+        $span.prepend($("<img/>").attr({"src": $input.data("image-src")}));
+      }
+      $span.appendTo($label);
 
       return $item;
     },