Add Calculate_Mutation_Models Synapse workflow

[BrunoGrandePhD]

I have a working version of the Calculate_Mutation_Models Synapse workflow. I was able to test it with the parameters below. Before submitting this PR, I will first try to add a checker workflow to ensure that the md5sum for the output file from the tool is indeed b18d68337bd738d4e6a0caff584853f2 given the example input files.

{
    "synapse_config": {
        "path": "/Users/bgrande/.synapseConfig",
        "class": "File"
    },
    "features_synapse_id": "syn22344112",
    "groups_synapse_id": "syn22344113",
    "mutations_synapse_id": "syn22344114",
    "output_parent_synapse_id": "syn22310623",
    "output_file": "mutation_models.tsv",
    "input_file_type": "tsv",
    "output_file_type": "tsv",
    "num_significant_digits": 6
}

N.B. The name of the tool has been harmonized to calculate_mutation_models and the output to mutation_models.

[BrunoGrandePhD]

I'm marking this PR as ready for review. I was able to add a checker workflow for the calculate_mutation_models tool (but not the workflow because of the issue of Synapse authentication).

@andrewelamb: Note that I had to fix a minor typo in the utils md5sum_checker.cwl tool to make it work when the working directory isn't the root. Let me know if you expect this to cause issues elsewhere in the repo.

[andrewelamb]

Looks good! I'm going to accept, but I think we should update the synstore and syn get tools to the latest release