Split the marine transport / deposition process into several ones

[benbovy]

MarineSedimentTransport has many parameters. I'm wondering what is the percentage of use cases where all of them are needed, or otherwise if there is a number of cases where compaction and/or grain size differentiation (sand/silt) can be turned off.

Depending on this, probably a good idea for more clarity would be to specialize MarineSedimentTransport into a hierarchy of processes with increasing complexity, like it has been done with StreamPowerLaw. This is only a change in API, internally all processes would call the same (most specialized) routine.