added gru_actor to makefile

build/includes/global/message_atoms.hpp

build/includes/gru_actor/gru_actor.hpp

build/includes/gru_actor/gru_actor_subroutine_wrappers.hpp

build/includes/gru_actor/gru_data_structure.hpp

build/makefile

build/source/actors/gru_actor/gru_actor.cpp

build/source/actors/gru_actor/gru_actor.f90

build/source/actors/job_actor/job_actor.cpp

utils/laugh_tests/celia1990/output/runinfo.txt

...celia1990/output/summa-actors_celia1990GRU1-1_timestep.nc