DISCO: import UCSC genome build map

We should import the definitions used by UCSC to describe their genomic builds, which map to specific original source builds.

These could be fetched via the UCSC open mySQL db.

See http://genome.ucsc.edu/goldenPath/help/mysql.html

it would be pulling in the dbDb table, from the hgcentral database. unfortunately, the references to source databases is really free text, which is not ideal. but it tells us something.