Update modal dust partitioning for wet and dry deposition

[fvitt]

What is the feature/what would you like to discuss?

The current dry and wet deposition code crudely maps the modal aerosol dust in MAM onto the 4 bulk size bins. A code by Mark Flanner is using erf functions to partition the lognormal distribution into the 4 sectional bins, which maps of the modal size distributions more precisely to the size bins required by the land and ocean models.

Is there anyone in particular you want to be part of this conversation?

@tilmes

Will this change (regression test) answers?

Yes

Will you be implementing this enhancement yourself?

Yes, but I will need some help