Show a single variant.

def variant(case_id, variant_id):
    """Show a single variant."""
    case_obj = app.db.case(case_id)
    variant = app.db.variant(case_id, variant_id)
    if variant is None:
        return abort(404, "variant not found")

    comments = app.db.comments(variant_id=variant.md5)
    template = 'sv_variant.html' if app.db.variant_type == 'sv' else 'variant.html'
    return render_template(template, variant=variant, case_id=case_id,
                           comments=comments, case=case_obj)