add internal ability to disaggregate catchment scalar forcings to hrus to allow for snowband usage

[andywood]

The snow17 code has the ability to simulate snowbands, a vector discretization of the catchment average simulation.
The framework only provides scalar catchment forcings, but these could be simply disaggregated (eg with a temperature lapse rate) to allow for snowband simulation. This would allow for testing sub-grid/sub-catchment simulation capabilities.