Unit prefixes and complex units in the GUI

Part of #798 (closed)

For the use of the ELN we are slowly diverging from the "only SI units" and no "unit prefixes (milli, kilo, etc.)". This causes issues in the GUI. While pint is mostly working fine, the GUI unit systems seems to have different troubles.

Here are a few comments by @josma

I have been exploring the issues with including the units with 'milli' and so on as part of the schema. To be able to do so, these units need to be registered in /home/pepe_marquez/NOMAD/nomad/nomad/cli/dev.py in two places, the unit_map and the unit_table.

Update: what is mentioned above worked for me for example for mA unit='milliampere' or mV unit='millivolt'. When I had something like unit='milliampere / centimeter / centimeter' or unit='milliampere * centimeter ** (-2)' the gui was giving me an error telling me that could not render the section.

@himanel1 could you investigate a bit and tell us what the GUI limitations are, which can be overcome, and which a systemically inevitable?