Merge pull request #25 from rolk/025_src

Upscale source terms
Add boundary conditions to upscaling constructor

The boundary conditions that the wrapper receives is forwarded to the
constructor of the upscaling object. (It does not yet do anything with
those conditions).
Throw an exception if other condition than no-flow

This will at least make sure that we don't run the model with incorrect
assumptions.
Return no-flow boundary conditions through accessor

There is an accessor in the upscaling object for getting the set of
boundary conditions to use on the upscaled grid. Currently we just
return a predefined set of no-flow conditions.