[A] PD: Parse output section; Add output_file_prefix.
[PL] Pass output stream to Process::post().
[PL] GW: Add output in post().
Merge pull request #533 from endJunction/bc

Dirichlet boundary condition for GroundwaterFlowProcess.
Merge pull request #534 from endJunction/SimulationOutput

Simulation output
Merge branch 'test-improvements' into develop