In flow conditions

[einola]

In the case of a regional model, we need to have the appropriate inflow conditions. These should ideally be one of the following:

• Zeros for all variables
• User-supplied constants for all variables
• Spatially variable field, read in from file
• Time and space varying field, read in from file

Main tasks:

• [ ] Make sure dynamics and advection can handle inflow on the boundaries
• [ ] Implement input for boundary conditions, as per the list above

[einola]

We'll do this as part of the MPI work: The inflow conditions are set on the halo and the dynamics does nothing extra.