Splitting the overly large radiation module into four parts:

radiation_sizes: size parameters and setup_scaling_factors (which
  depend on the sizes)
radiation_sed_parameters: routines to determine the SED settings and
  properties (BB and PL for the moment)
radiation_tables: calculate the photoionization and heating rate
  tables (as function of optical depth and frequency subband)
radiation_photoionrates: look up the photoionization and heating
  rates from the tables.

This involves changes in the use commands in doric.f90,
files_for_3D/C2Ray.F90 files_for_3D/Makefile
files_for_3D/evolve8.F90 files_for_3D/output.F90
files_for_3D/photonstatistics.f90

For other problems than cubep3m (3Dm) the corresponding modules
still need to be fixed.

Test for the standard test and found to produce identical results
to the old "monolithic" radiation module.