Create method to group bigbed features

[cmdcolin]

BigBed gene grouping is sort of difficult since there is no gene hierarchy indicating transcript children, so currently BigBed transcripts of the same gene arent loaded into a single gene glyph

Could add custom grouping by name possibly requiring refetch

[cmdcolin]

Note that biodalliance kind of has a weird approach where their genes track is semi-collapsed by default (same as jbrowse style collapse, except only on a per-gene basis) and then a "+" button on their track label expands all the transcripts from a gene