Add selector classes to the top level widget, fixes #22
Add selector classes to the top level widget, fixes #22

jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser