#960 fix event handling for FF

- use cross browser `event.target` instead of IE-specific
`event.srcElement`

ng2-components/ng2-alfresco-datatable/src/components/datatable/datatable.component.spec.ts

@@ -314,26 +314,26 @@ describe('DataTable', () => {
 
     it('should replace image source with fallback thumbnail on error', () => {
         let event = <any> {
-            srcElement: {
+            target: {
                 src: 'missing-image'
             }
         };
 
         dataTable.fallbackThumbnail = '<fallback>';
         dataTable.onImageLoadingError(event);
-        expect(event.srcElement.src).toBe(dataTable.fallbackThumbnail);
+        expect(event.target.src).toBe(dataTable.fallbackThumbnail);
     });
 
     it('should replace image source only when fallback available', () => {
         const originalSrc = 'missing-image';
         let event = <any> {
-            srcElement: {
+            target: {
                 src: originalSrc
             }
         };
 
         dataTable.fallbackThumbnail = null;
         dataTable.onImageLoadingError(event);
-        expect(event.srcElement.src).toBe(originalSrc);
+        expect(event.target.src).toBe(originalSrc);
     });
 });

ng2-components/ng2-alfresco-datatable/src/components/datatable/datatable.component.ts

@@ -146,7 +146,7 @@ export class DataTableComponent implements OnInit, AfterViewChecked {
 
     onImageLoadingError(event: Event) {
         if (event && this.fallbackThumbnail) {
-            let element = <any> event.srcElement;
+            let element = <any> event.target;
             element.src = this.fallbackThumbnail;
         }
     }