createDropzone() {
		const dropCtrl = new SimpleDropzone(this.dropEl, this.inputEl);
		dropCtrl.on('drop', ({ files }) => this.load(files));
		dropCtrl.on('dropstart', () => this.showSpinner());
		dropCtrl.on('droperror', () => this.hideSpinner());
	}
Sets up the drag-and-drop controller.