add .tsv extension (tab-separated values) to list of valid input files

[FelixBaensch]

I would summarize this under the topic of delimiter separated values (dsv).

[JonasSchaub]

Good point. Is ".dsv" also a common file extension for this purpose?

On the other hand, for the export, we always talk about exporting CSV but the separator/delimiter can actually be set to sth else.

[FelixBaensch]

I don't know if .dsv is a common file extension. I would rather handle everything under the hood of csv but also allow the import of tsv, etc.

[JonasSchaub]

I don't know if .dsv is a common file extension. I would rather handle everything under the hood of csv but also allow the import of tsv, etc.

Exactly, I agree.