data: import snaptron

[buchanae]

Snaptron provides a large set of exon-exon splice junctions from a large number of human samples. It also includes expression profiles.

https://academic.oup.com/bioinformatics/article/34/1/114/4101942
http://snaptron.cs.jhu.edu/

Questions remain about how to appropriately link this to the graph. These probably shouldn't be linked directly to grc37/38 genes, as the junctions might not match those annotations.