Added a fixed Pint unit and constant file, added CLI command for creating unit conversion data for the GUI, added new React component for changing the units in the ArchiveBrowser.

The CLI command nomad dev units outputs a Javascript source file that is automatically created from the currently used Pint units. This command is also run in the Dockerfile.

I added a menu for choosing the units in the ArchiveBrowser. You can either select SI units, atomic units, or a custom selection for a selection of quantities. By default, a custom selection is used (eV instead of Joule, angstrom instead of meter, otherwise default SI units). This can be changed based on what we think is reasonable.