Add test for UTF-8 encoding issue from Excel

Migrated from https://github.com/VariantEffect/MaveDB/issues/192, we should make sure this isn't an issue with mavedb-api.

Some versions of excel generated csv files contain a byte ordering mark that creates an invalid heading name (eg \ufeffhgvs_pro)

Files should be opened with a utf-8-sig decoder to avoid this issue