wrapper for zarp execution

wrapper in the prepare_inputs.py for executing zarp additional options added: --execution_env (allowed values local or slurm or none for now) --snakefile_path path to the snake file --bindings paths to be included in the singularity --cluster_json path to the cluster.json (used in the slurm run)

Fixed also a test_zarp_wrapper test (this needs to be refactored and be merged with existing tests) Fixes #130 (closed)