fewer JOINS and make sure to pull all of the background (#221)
fewer JOINS and make sure to pull all of the background (#221)

(previously we were only pulling backround counts where the sample
had a count;  moving the background_id constraint to the ON clause
of the left outer join fixes that)
chanzuckerberg/idseq-web,chanzuckerberg/idseq-web,chanzuckerberg/idseq-web,chanzuckerberg/idseq-web,chanzuckerberg/idseq-web