loc_conc_BC is not necessary. Therefore remove it.
The time stepping scheme is changed to adaptive time stepping.
Much better performance while simulating monod2d.
The variable _I_NMin_bar is now removed.
In the local problem, we explicitly use _I_mob, _I_sorp, _I_min and _I_kin.
For the primary variable vector u_unknowns, the mob and sorp components are in natural log scale,
while the min and kin components are in linear scale.
All input and out put interfaces are changed accordingly.
remove _I_NMin_bar, use _I_sorp and _I_kin accordingly.
remove the get function of _I_NMin_bar, add get function for _I_kin.
no longer use _I_NMin_bar, instead using _I_sorp and _I_kin.
same convergence criteria for local problem.