First merge of LPJ-GUESS state updating code

[MagicForrest]

Description

Functions for updating LPJ-GUESS state for use with the SDA. The allocation() function is C++ ripped from the model, the allometry() function(much simpler) was recoded. Also include is a function so sum LPJ-GUESS per PFT vegetation state variables to the gridcell level and a simple function to scale the density of individuals in a cohort (and the associated C and N pools). The master function updateState.LPJGUESS() can be called should be called after the SDA has been carried out.

Conspicuously missing from this update is the ability to iterate with new values of biomass and density if the update produces an abnormal individual, and code from produing individuals of an entirely new PFT.

Motivation and Context

Essential for LPJ-GUESS SDA.

Review Time Estimate

• [X ] Niao!
• Within one week
• When possible

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [X ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• [ X] I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.