Support for photometric units

[noah1510]

Photometric units require conversion function that takes the wavelength into account.

• create the json files and formats for the photometric sensitivity functions
• (optional) create lower accuracy variants to reduce the code size (e.g. for arduino)
• update the unit json format to link photometric units to their non photometric equivalent
• update the generator templates
  • Update C++
  • Update python
• update all the documentation

Once this is done every physical unit should be able to be added to the unit system library