Fix runtime errors...* wqflask/wqflask/__init__.py: when registering a URL, the url_prefix
should begin with a trailing slash.
* wqflask/wqflask/jupyter_notebooks.py: fix imports.
Build UI for Jupyter Notebooks Launcher...* Build a HTML UI for the Jupyter Notebooks Launcher feature that fits
in, aesthetically, with that of the whole GeneNetwork look and feel.