Added ability to add css class to data provider options.

You can now add a class option to a node of the data provider options and it will be appended to the list item.

dist/js/bootstrap-multiselect.js

@@ -252,6 +252,11 @@
             optionLabel: function(element){
                 return $(element).attr('label') || $(element).text();
             },
+
+            optionClass: function(element) {
+                return $(element).attr('class') || '';
+            },
+
             /**
              * Triggered on change of the multiselect.
              * 
@@ -675,12 +680,14 @@
 
             // Support the label attribute on options.
             var label = this.options.optionLabel(element);
+            var classes = this.options.optionClass(element);
             var value = $element.val();
             var inputType = this.options.multiple ? "checkbox" : "radio";
 
             var $li = $(this.options.templates.li);
             var $label = $('label', $li);
             $label.addClass(inputType);
+            $li.addClass(classes);
 
             if (this.options.enableHTML) {
                 $label.html(" " + label);
@@ -1220,6 +1227,7 @@
                         value: option.value,
                         label: option.label || option.value,
                         title: option.title,
+                        class: option.class,
                         selected: !!option.selected,
                         disabled: !!option.disabled
                     });