add co2 equivalences in text report

[Bastian-Eisenmann]

Text report does now also contain some information about CO2 equivalences like:

Which equals:

• {n} km travelled by car
• Monthly co2 absorption of {m} trees
• {o} flights from paris to London
• {p} % of a flight from paris to london
  --
  Note: Only either the absolute or the relative flight equivalent is shown in the output.

[tillenglert]

Apart from my comment, looks good!