New database version for perennial crops

includes also sugar cane
Update of CO2 emission algorithm

Potential error with SMB maintenance respiration and organic pools
turning negative has been fixed.
Update of CO2 emission algorithm

adds to earlier commit
MONICA Perennial crop module

A major version update for perennial crops towards MONICA 2.0 - Test
version for Leonardo comes with sugar cane crop in a new database
version. From here, MONICA uses the json input file format!