Single and multi-phase flow with Finite Volume

[ajacquey]

Implementation of single-phase and multi-phase flow using finite volumes.

• Single phase flow.
• Multi phase flow.
• Solute transport.

[ajacquey]

Still to do:

• Check slow solve with FV (see fv_single_phase_1D_transient.i for example)
• Formulation for multiphase + solute.
• Tests for multiphase flow (e.g. buckley-leverett.i and Mose.i)

[ajacquey]

There is a bug in the FV formulation.
This causes a segmentation fault when running with several MPI processes.