De-dup the list of samples in result

Right now `samples` key is an alias for `solutions` list. `solutions` is returned by SAPI, and we introduced `samples` as it sometimes makes more sense from user's perspective.

Now that we're implementing pre/post-processing of parameters/response (see #199, #200), it makes sense to have `samples` be a list of dictionaries which will map *only active* qubits to states.