Update from v1.0.0: Outsource init and primary particle preparation to modules

Update from v1.1.0:
In order to facilitate easier maintenance, the initialization and primary particle preparation has been outsourced from the wrapper for iHAMOCC into a bit more general modules for HAMOCC-like models, which should ease the re-use of those routines for other OBGC models based on HAMOCC.
At initialization:

• init_m4ago_nml_params
• init_m4ago_derived_params

(in this order) from mo_m4ago_HAMOCCinit.F90 needs to be called.

Then, at run time, a wrapper calls

• prepare_primary_particles (from mo_m4ago_HAMOCCPrimPart)
• mean_aggregate_sinking_speed (from mo_m4ago_core)

to eventually calculate the mean sinking velocity of particles.

Updated M4AGO sinking scheme

This release provides the M4AGO code as originally published in Maerz et al. 2020 in a restructured form with minor modifications (see below).

Modifications carried out to the version used in Maerz et al. 2020:

• a safety minimum molecular dynamic viscosity value is introduced to avoid negative values for extreme temperatures outside the range of the original formulation for the molecular dynamic viscosity
• small modification in how the number of primary particles is calculated
• small modification in how the aggregate stickiness is calculated
• improved encapsulation for OMP threading
• improved the code to avoid potential NaNs in case of zero concentrations

In summary, the modifications led to changes of the mean sinking velocity of order 1e-9m/d, which is negligible compared to regularly calculated sinking velocities of order 10m/d and does not affect previously published results.