Unit conversion for transportation service output needs to be fixed

[rplzzz]

Freight should be able to convert mass units, and both passenger and freight will fail if you try to convert to tonne-km or passenger-km (i.e., without a count unit).

[xavier-gutierrez]

I asked Nazar what are common units for freight service to be requested in. his template only needed counts conversion for the service output variable. right now, weight conversions are only needed for pm-emissions, which handles the units kt and Mg. are there specific units you want in the conversion matrix?

[xavier-gutierrez]

Added functionality to count conversion where if no 'counts' unit is detected, the output/input unit will be identified as unity and converted as such. I throw a message that such a conversion is taking place since in all the other unit conversions, there is a warning if no match is found in the conversion matrix. This is updated in the transportation branch