createViewer() {
		this.viewerEl = document.createElement('div');
		this.viewerEl.classList.add('viewer');
		this.dropEl.innerHTML = '';
		this.dropEl.appendChild(this.viewerEl);
		this.viewer = new Viewer(this.viewerEl, this.options);
		return this.viewer;
	}
Sets up the view manager.
@return {Viewer}