Support to include comparative response for flights

Fixes #66 (closed) and add support for comparative responses of flights in the reverseLookupManager. Comparative emission results provide the conditions under which the same emissions will be produced in a different context. These help the user to better internalize the emissions in terms of some other more relatable entity for emission. The reverselookup support for trees, vehicles, and trains are already present. A reverselookup support for flights will widen the variety of comparative results that the user will get.