RT GEAR thermochemistry first attempt

configure.ac

doc/RTD/source/RadiativeTransfer/GEAR_RT.rst

...es/RadiativeTransferTests/Advection_1D/rt_advection1D.yml

...es/RadiativeTransferTests/Advection_2D/rt_advection2D.yml

...nsferTests/IonizationEquilibriumICSetupTest/ion_equil.yml

...RadiativeTransferTests/RandomizedBox_3D/randomized-rt.yml

examples/RadiativeTransferTests/StromgrenSphere_2D/makeIC.py

...es/RadiativeTransferTests/StromgrenSphere_2D/makemovie.sh

...RadiativeTransferTests/StromgrenSphere_2D/plotSolution.py

...veTransferTests/StromgrenSphere_2D/stromgrenSphere-2D.yml

...veTransferTests/StromgrenSphere_3D/stromgrenSphere-3D.yml

...erTests/UniformBox_3D/uniform_rt_timestep_output_sync.yml

examples/parameter_example.yml

src/Makefile.am

src/hydro/Gizmo/hydro_iact.h

src/kick.h

src/rt/GEAR/rt.h

src/rt/GEAR/rt_additions.h

src/rt/GEAR/rt_blackbody.h

src/rt/GEAR/rt_flux.h