vector aggregate needs update to account river class aggreagation

[fuadyassin]

No description provided.

[mee067]

MERIT-hydro BASINS has order for each river segment and delineations from MERIT-hydro DEM or other DEMs can produce river orders. River orders can be used as river classes in MESH, and possibly other models. River classes can be assigned different parameters (roughness: R1N, R2N, and shape parameters AA1 .. 4) if desired. This gives more degrees of freedom when calibrating routing. The assumption is that larger rivers behave differently from smaller ones and river order reflects this nicely for vector-based setups. When rivers and basins are aggregated, river orders change and this needs to be handled by the aggregation script.