Initial ExpressionMatrix module

Here's the initial module containing the R pipeline script.  I think we may want to rename the module to avoid confusion with LabKey's microarray module that contains an ExpressionMatrix assay.

Also, I couldn't figure out how to get R to write a matrix tsv where the probe id rownames column has a header -- it's just blank.  To get the import to succeed, the probes need a header of 'ID_REF'.