Retrieve all variant callers for somatic calling, handling somatic/germline.

def get_somatic_variantcallers(items):
    """Retrieve all variant callers for somatic calling, handling somatic/germline.
    """
    out = []
    for data in items:
        vcs = dd.get_variantcaller(data)
        if isinstance(vcs, dict) and "somatic" in vcs:
            vcs = vcs["somatic"]
        if not isinstance(vcs, (list, tuple)):
            vcs = [vcs]
        out += vcs
    return set(vcs)