Second stage calib extra config option.

Initial timber forest area from Schulze et al. 2019.

Improved handling of wood imports during calibration.

Minor bug fixes.
Merged new changes from master.

Updated land cover age file.
Energycrop demand previously not carried through to GAMS.

Various fixes.
Code cleaned up.

Unavailable area adjustment.

Changes to protected area calculation and update.

Wood yields and C flux bug fixes.

Changes to avoid reading in all wood yield and C flux data.

Now keeping track of tiles within grid cells and time since conversion.
Refactored ForestManager.
Cleaned up some data structures.