Validator option for the different flavors

[jpfeuffer]

If you want to convert to openms or mq, there might be more restrictions on certain columns and entries like modifications or TMT channel nomenclature. We should make sure that those can be validated as well.

Also I am not sure if validation does that already:
Warn if channels are not complete per (raw) file. I think we should enforce that, even if one would need to provide dummy samples if that channel is really not used (which is rarely the case)