Modify snp_allele_frequencies to allow investigation of any genomic region.

[KellyLBennett]

Currently SNP tables can be generated but require a transcript as an input parameter which restricts its use to coding regions. However, there are cases for looking at regions lying outside of genes and therefore it would be useful to modify the function to look at any genomic region input. Since snp_calls can already take a region (or transcript) as a parameter, this would require changes to the code adding the effect annotations and the creation of the title only (could be generated only if a transcript is used).

[leehart]

Needs further discussion.