Check for PETSc first

Until we overhaul the solver input options
Need to init some TimeSolver

This is because I was stupid and tied MultiphysicsSystem too closely
to the Solver. At least left some \todo's to fix this, but for the
time being, create a dummy SteadySolver that won't be used so we
can test the PETScSNESSolver.
Need to init the EquationSystems object
Correct point range for PetscSection