Reduce duplication of rRNA data in genome browser

[blakesweeney]

Currently the genome browser contains lots and lots of 'extra' entries for certain RNA types. A nice example is: https://rnacentral.org/rna/URS0000726FAB/9606. Here the browser is nearly useless because of all the minor sequence variants and fragments found. We can clean this up by hiding things which are fragments and minor sequence variants. The first step should just be to detect when a sequence is overlapping another one and has some issue that indicates it should not be displayed (qa issues, unexpected gaps, size, etc).