Consider relaxing the Sampler.parameters API

[arcondello]

Application
At the moment, the Sampler ABC asks that the Sampler.parameters attribute be a dict of the form {kwarg: [relevant_property, ...], ...}. In practice though we rarely use the relevant properties list and almost all samplers look like {'beta_range': [], 'num_reads': []}

Proposed Solution
I propose that Sampler.parameters should return a Collection of accepted sampler arguments. This supports our current form but the above example could instead be {'beta_range', 'num_reads'}.

[arcondello]

We could also by default use inspect to populate the parameter.