unify igvShiny and igvR GWAS track APIs

[paul-shannon]

@vjcitn @stankiewicz565

Vince and Sara,

May I get your suggestions on unifying the GWASTrack APIs in igvR and igvShiny?

Here is what we have now:

igvShiny::GWASTrack <- function(trackName, data, chrom.col, pos.col, pval.col,
                                trackHeight=50, autoscale=TRUE, minY=0, maxY=30)

    igvR::GWASTrack <- function(trackName, table, chrom.col, pos.col, pval.col,
                                color="darkBlue", trackHeight=50, visibilityWindow=100000)

 igvR::GWASUrlTrack <- function(trackName, url, chrom.col, pos.col, pval.col,
                                color="darkBlue", trackHeight=50, visibilityWindow=100000)

The igvShiny version is most recent. data can be either a data.frame or a url, eliminating the need for two constructors.

Perhaps add color and visibilityWindow from igvR into the igvShiny version, then reuse that expanded API in single merged igvR version?

I am happy to do this, but need your views, and your assessment of benefit to your work, before jumping in.