Normalized dates are set to approx.

Some of the normalized dates (persons and sources) seem to be set to 'approx.' by default. Some seem to entries where whether 'range' nor 'approx.' options were selected. See e.g.: https://corpus-musicae-ottomanicae.de/receive/cmo_person_00000292 https://corpus-musicae-ottomanicae.de/receive/cmo_source_00000064

But in the following case, probably 'range' was selected originally: https://corpus-musicae-ottomanicae.de/receive/cmo_source_00000059

This effects especially older entries, since we might have to go back to each dataset and correct them.