Moving estimators increments from radiation into subroutines (estimators for PPL ionization solver and IP)

[jhmatthews]

Currently we duplicate code between radiation() and bf_estimators_increment(), which are the corresponding routines which increment estimators in non-macro atom and macro atom mode when a photon travels ds inside a cell.

To avoid this, I've moved all the duplicated incrementing to a subroutine called update_banded_estimators(). This routine

• updates j, j_direct, j_scatter
• updates ip, ip_direct, ip_scatter
• updates the banded estimators we use e.g. xave_freq, xj etc for each band
• updates n_ds, mean_ds and ave_freq

I've also moved the part where photon stats are saved to a file as part of Extra_diagnostics to a new subroutine called save_photon_stats.

This shouldn't change how anything works and is merely to avoid duplication. Only files modified are radiation.c and estimators.c

[jhmatthews]

I've tested this with a fiducial model, it produces identical answers so merging into dev.

dotted lines and solid lines show before and after for three random cells. Numbers have also been checked.