efficiency modifications and refactoring of mo_graupel

routine was optimized so that precipitation fluxes are only calculated in columns with condensate, and only over a height that extends to highest most condensate.

code was cleaned up to remove unnecessary variables and to more compactly organize its computations.

use of aes_thermo rourtines was restored, which required the addition of the mo_aes_thermo.f90m module to this library.

elemental routines were redefined as pure as the elemental function is not needed and complicates the open_acc implementation

modifications make the code considerably faster.