Checkout a new branch or checkout to a branch for a given issue.

def checkout(accountable, issue_key):
    """
    Checkout a new branch or checkout to a branch for a given issue.
    """
    issue = accountable.checkout(issue_key)
    headers = issue.keys()
    rows = [headers, [v for k, v in issue.items()]]
    print_table(SingleTable(rows))