small updates for file names of source derivatives for adjoint simulations
updates file i/o units; prettifies code
synchronizes gpu loading
prepares GPU buffer for checking wavefield norms at timestamps
Switched request file write to a parallel write (one file per region).

Replaced serial request read with parallel request read.

Fixed up the reading in of the new cem model

Switched request file write to a parallel write (one file per region).

Replaced serial request read with parallel request read.

Fixed up the reading in of the new cem model
Cleaned up merged version of model_cem.f90 a bit.
Brought model_cem back up to fortran 2003 standard.
added a comment from Daniel Peter