Added emit function to Dropzone

See the docs for some [examples using emit](https://github.com/enyo/dropzone/wiki/FAQ#how-to-show-files-already-stored-on-server)
I can't find any other usage so this covers the two events that I am aware of: `addedfile` and `thumbnail`

dropzone/dropzone.d.ts

@@ -72,6 +72,8 @@ declare class Dropzone {
     getRejectedFiles(): DropzoneFile[];
     getQueuedFiles(): DropzoneFile[];
     getUploadingFiles(): DropzoneFile[];
+    
+    emit(eventName: string, file: DropzoneFile, data?: string);
 }
 
 interface JQuery {