Speed up udf_GeneSymbol

[zx8754]

https://github.com/oncogenetics/LocusExplorer/blob/master/Source/UDF.R#L31

[zx8754]

Maybe collapse ("TxDb.Hsapiens.UCSC.hg19.knownGene", "org.Hs.eg.db") and save as RData.

[zx8754]

oncogenetics/oncofunco#3