General Hi-C geom

[teunbrand]

It should take up to two experiments and a GRanges region as input. Would output a matrix or polygon, depending on the parameters. Ideally, there would be a plot-wide setting for the regions that the geom could inherit and apply. Could maybe add options to allow chromosomes to be columns, for facetting purposes, and add custom facet parameters to be passed on as a named vector.