Add minimumInputLength option

Shoul be added as "minimum-input-length" on ui-select-choices directive

Author: giorgiofellipe

src/uiSelectChoicesDirective.js

@@ -54,7 +54,11 @@ uis.directive('uiSelectChoices',
         scope.$watch('$select.search', function(newValue) {
           if(newValue && !$select.open && $select.multiple) $select.activate(false, true);
           $select.activeIndex = $select.tagging.isActivated ? -1 : 0;
-          $select.refresh(attrs.refresh);
+          if (!attrs.minimumInputLength || $select.search.length >= attrs.minimumInputLength) {
+            $select.refresh(attrs.refresh);
+          } else {
+            $select.items = [];
+          }
         });
 
         attrs.$observe('refreshDelay', function() {