Shade the "intron" skips in RNA-seq reads according to XS/TS/ts tag

[cmdcolin]

The arcs on the SNPCoverage track are already default colored according to these tags, could also color the intron skips in the read pileup also. this would reveal which reads are contributing to a particular strand or splice pattern (helps especially if there are reads from a reverse strand and forward strand gene overlapping)

[cmdcolin]

there is another possible subtext which is: making this the default coloring when RNA-seq is detecting. currently the default coloring is just the "grey boxes" but it could be that the coloration of strand is a good default if it is 'detected to be RNA-seq'