More flexible properties for metainfo
This came up as part of #672 (closed)
Support for TEMPLATE_properties (currently done via sub sections). Allow properties that are named in the data. This would also allow sections that are similar to a dictionary.
support for arbitrary attributes on quantities (currently done via sub sections). Simple attributes on quantities would allow to characterise quantities better.
support for dynamic units. Currently archive data is always given in SI units. We might want to store data in different units, but the data would need a mechanism to provide the actual unit.