SampleSet.from_samples_bqm should officially support BinaryPolynomials

`SampleSet.from_samples_bqm` accepts any object that has a `.energies` method and a `vartype` attribute instead of just BQMs, most notably `BinaryPolynomial`.

https://github.com/dwavesystems/dimod/blob/15e6f93638b937156e8f0fff008c3b63a451aa45/dimod/sampleset.py#L417

The docstring should mention this and tests should be added to check for backwards compatibility. I don't think the name of the method should be generalised, as this is just using python's duck typing.