Add new notebook, add informative text to other notebook

[ariedel]

This PR has:

• The new Pandeia GUI
• The helper library for the Pandeia GUI (which will be part of mainline Pandeia in the v1.4 release), modified to not offer any options not available in Pandeia v1.2.2
• New help text for detector setups and defaults set appropriately
• New help text and defaults for detector setups in the old Pandeia python-based-interface notebook too.
• Slight modification to the Getting Started notebook, so it points to all the Pandeia notebooks.