Load the map files "tdmMapDesign.csv" and optionally
also "userMapDesign.csv" and store them in tdm$map and tdm$mapUser,
resp. These maps are used by tdmMapDesApply.
"tdmMapDesign.csv" is searched in the TDMR library path find.package("TDMR").
(For the developer version: <tdm$tdmPath>/inst).
"userMapDesign.csv" is searched in tdm$path (which is getwd() if the user did not define tdm$path).
tdmMapDesLoad(tdm = list())list, needed for tdm$tdmPath and tdm$path
tdm, the modified list with new elements tdm$map and tdm$mapUser