Make it possible to flip alleles with only a z-score column, or without a frequency column

[Joannavonberg]

As for your question whether it's a problem to already have a z-score column in your dataframe / tibble: I suspect not, but the function will not change anything to your z-column. It actually expects there to be a "freq", "beta" and "se" column and changes these according to the flipped alleles. I do see the need for a new version of this function that can work without an allele frequency column (because PolarMorphism doesn't need it), and a version that can work with only z-scores if beta and se are not available. I'll think about adding this functionality, and I'll create a new issue for this

Originally posted by @Joannavonberg in #5 (comment)