Refactor loadingTemplate to abstract class

app/assets/javascripts/filtered_search/dropdown_assignee.js.es6

@@ -17,10 +17,7 @@
             current_user: true,
           },
           searchValueFunction: this.getSearchInput,
-          loadingTemplate: `
-          <div class="filter-dropdown-loading">
-            <i class="fa fa-spinner fa-spin"></i>
-          </div>`,
+          loadingTemplate: this.loadingTemplate,
         }
       };
     }

app/assets/javascripts/filtered_search/dropdown_author.js.es6

@@ -17,10 +17,7 @@
             current_user: true,
           },
           searchValueFunction: this.getSearchInput,
-          loadingTemplate: `
-          <div class="filter-dropdown-loading">
-            <i class="fa fa-spinner fa-spin"></i>
-          </div>`,
+          loadingTemplate: this.loadingTemplate,
         }
       };
     }

app/assets/javascripts/filtered_search/dropdown_label.js.es6

@@ -10,10 +10,7 @@
         droplabAjax: {
           endpoint: 'labels.json',
           method: 'setData',
-          loadingTemplate: `
-          <div class="filter-dropdown-loading">
-            <i class="fa fa-spinner fa-spin"></i>
-          </div>`,
+          loadingTemplate: this.loadingTemplate,
         },
         droplabFilter: {
           filterFunction: this.filterWithSymbol.bind(this, '~'),

app/assets/javascripts/filtered_search/dropdown_milestone.js.es6

@@ -10,10 +10,7 @@
         droplabAjax: {
           endpoint: 'milestones.json',
           method: 'setData',
-          loadingTemplate: `
-          <div class="filter-dropdown-loading">
-            <i class="fa fa-spinner fa-spin"></i>
-          </div>`,
+          loadingTemplate: this.loadingTemplate,
         },
         droplabFilter: {
           filterFunction: this.filterWithSymbol.bind(this, '%'),

app/assets/javascripts/filtered_search/filtered_search_dropdown.js.es6

@@ -9,6 +9,9 @@
       this.hookId = 'filtered-search';
       this.input = input;
       this.dropdown = dropdown;
+      this.loadingTemplate = `<div class="filter-dropdown-loading">
+        <i class="fa fa-spinner fa-spin"></i>
+      </div>`;
       this.bindEvents();
     }