Add biomass due to extra resources (extra biomass) as an output option

[kpalmqui]

If xres = 1 and xgrow > 0, then temporary biomass due to extra resources will be added for each species when extra resources are available.

To help us understand the contribution of this "extra biomass" to total biomass, it would be useful to add a flag in inputs to output extra biomass seperately, which is the goal of this issue.

One possibility is to include extra biomass as a new column for every species within the biomass output file (bmassavg.csv) when the flag is set to 1.