Default to using the biomart file found in ./bin, recreate in workdir if asked.

[inmanjm]

Currently the pipeline is using ensg.genes if it exists in the working directory. It should default to looking for it in the ./bin dir. There should be a way to have it copy the file into the workdir; and retain the ability to have it newly created, if desired.

[inmanjm]

Now expects Biomart_hsapiens_ensembl_gene_symbols.csv to be present in working dir. Can also be directed to use a different file, or re-generate it using the original code that builds the mapping based on the genes present in the first sample's input .csv