allow users to fetch other ucsc gene prediction tables

[alexg9010]

right now we are enforcing knownGene, but if we use webfetch from UCSC directly, other tables should be possible, i.e. refGene ...

pigx_bsseq/scripts/fetch_procedures.R

Line 117 in 11f4260

if(!(type %in% c("cpgIslandExt", "knownGene"))) {