Add operator-ket and operator-bra support to super_tensor.

See #238 for more details, but this extends ``_permute`` and ``super_tensor`` to act correctly on ``operator-ket`` as well as ``super, superrep="super"``.
That's a good point. I forgot to do so in modifying code that predates that, but I agree: ideal time to make it more robust that way. I'll modify and revise the PR, then.