Fix/aron conversions

Aron conversions of enums cause errors due to the enums being converted to empty dictionaries. In case of other conversions, it is difficult to see where errors come from, if they originate from int64 vs. plain int or, lesser, from double vs. float differences. This merge request tries to

• Fix existing problems
• Make detecting usage mistakes easier (although at the cost of some more checks)
• Make aron-related type conversions from common python types easier (e.g., specifying a time or pose using plain python float values)

Thanks @peller and @gao for help.

If @peller, @gao and/or @plewnia have objections regarding the changes, please feel free to communicate them so we can discuss how to do it in the best way!