Initial refinement (t0ref) for user defined problems does not take meshblock/box into account

[adityakpandare]

The initial refinement Refiner::t0ref() is triggered in the Refiner constructor. At this point, the discretization-child (ALECG) has not completed the box/meshblock initialization. So t0ref() does not refine based on the initial conditions set up in the meshblock/box block. This supports the argument that Refiner should not have separate logic for initial refinement (t0ref) and refinement during timestepping (dtref).