control strand type (RNA /DNA ) from config file

[Blosberg]

current assumption of RNA data is hard-coded.
upon conversion from table to GRanges (in tables2GR), the model parameters are stored explicitly, and "T" is transliterated to "U". The input variable strand_type="RNA" in the function writeout_pore_model() in Rmain_npreads_tables2GR.R is hardcoded to "RNA". We should instead refer directly to the read type defined in the config file whenever we need to start differentiating, just as we refer here for options during alignment in the solution to Issue #9

Very easy to fix, but no need to do so at the moment. Will revisit this whenever (if-ever) it becomes necessary to distinguish between RNA/cDNA/etc.