Optimize leaf angle distribution

[alkalifly]

LAD currently hard coded to 0.5

[aantonyb]

LAD is not a parameter in DALEC1100, following discussions we want to make this a free parameter (LAD prior range TBD).

[ebilir]

Currently a hard-coded LAD is used in the VegK calculation which occurs prior to declaring the pars structure. Hence in the current code configuration we can't call any optimizable parameters in the VegK calculation. The intent is to move the VegK computation later, but needs careful scrutiny of DALEC_1100_DATA structure and dependencies-- VegK is passed into this.