More helpful warning messages

[angiehjort]

when marker space is ["asylym_residence", "time"]
when encoding space is ["origin"] without a filter

there is a warning about joining two tables
would be helpful to instead complain about the keys and suggest that in this situation encoding turns into a constant, where origin needs to be specified further to a specific entity

or if it was an error and just an unintended mismatch of spaces
which it was in my situation (forgot to change after a copy-paste)