[ENH] `FASTA` to `String` converter

[satvshr]

@JaBirke @KubiczekD requested a FASTA to String converter so that they can load sequencing data they recieve from the lab, which is usually in the FASTA format.

[satvshr]

@JaBirke @KubiczekD any FASTA file we should add to the repository? (I need it for testing purposes)

[fkiraly]

I would suggest to:

• load this in the common format we agreed on in String transformations interface #106, i.e., have an option for list of str, and one for the format in String transformations interface #106 which is DataFrame of str
• we should not reinvent the wheel and use biopython where possible