Refactors posters to use decls (#8128)

* poster

* Moves decls_repo init forward

* Moves decl_repository init even further forwards

code/global_init.dm

@@ -21,6 +21,7 @@ var/global/datum/global_init/init = new ()
 	error_log = file("[log_path]-error.log")
 	debug_log = file("[log_path]-debug.log")
 	debug_log << "[log_end]\n[log_end]\nStarting up. [time_stamp()][log_end]\n---------------------[log_end]"
+	decls_repository = new()	
 	load_configuration()
 	makeDatumRefLists()