makes some changes to completed mapping files

Removes 'RCBarcode' and 'BarcodeName' columns and changes column header
'DNAconc(ng/ul)' to 'DNAconc'. Changes 'NA's in'HostSpecies' column to
'Control'.
Map alter script complete
changed to deal with mapping files being .tsv

map alter was originally meant to alter .txt files but the mapping
files have been changed to .tsv so I just had to make some minor
changes to the script.