[ADF-1097] Don't upload file if extension is not acceptable (#2143)

* FileModel's extension getter

* Filter out not supported extension from upload

ng2-components/ng2-alfresco-core/src/models/file.model.ts

@@ -73,4 +73,8 @@ export class FileModel {
             return v.toString(16);
         });
     }
+
+    get extension(): string {
+        return this.name.slice((Math.max(0, this.name.lastIndexOf('.')) || Infinity) + 1);
+    }
 }