FLASH4 complete API

  Performs Flash initializations, which includes:

  Call all 'init' routines in units, in the right order.
  Order does matter, particularly when restarting from a 
  checkpoint file.

  For the most part, Driver_initFlash calls another units' init
  routines directly, like call IO_init or call Grid_init.  This
  routine also makes calls to other Driver initialization routines
  like Driver_initMaterialProperties or Driver_initSourceTerms.
  These routines then call the unit-specific initialization 
  routines.  This level of abstraction was added to simplify
  the initialization calls.