Dwave-system

New Features
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* `draw_chimera_bqm` function to draw a Chimera-structured binary quadratic model.
* `common_working_graph` function that finds a graph with the nodes and edges common to two graphs.

Fixes
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* `chain_break_frequency` now correctly uses the number of occurrences in its calculations.
* `dwave.embedding.chimera.find_clique_embedding` now handles the K1 and K2 special cases and returns and embedding of optimal chain length.
* `TilingComposite` now propagates `SampleSet.info` returned by its child sampler.

New Features
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* `CutOffComposite` and `PolyCutOffComposite`
* Support 'nice' Pegasus labelling with `pegasus.find_clique_embedding`

Fixes
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* Remove dwave-networkx version upper bound to resolve version conflicts

Changes
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* Use the dwave.embedding namespace for embedding utilities rather than dimod.embedding
* Use dimod 0.8.x, especially `SampleSet` rather than `Response`.

New Features
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* dwave.embedding namespace
* `broken_chains` function to find broken chains in samplesets
* chain break resolution functions: `discard`, `majority_vote`, `weighted_random`, `MinimizeEnergy`
* `embed_bqm`, `embed_ising` and `embed_qubo` functions.
* `unembed_sampleset` function
* `target_to_source` function that determines the source graph from a target graph and embedding
* `chain_to_quadratic` function that finds the quadratic biases that induce a chain
* `chain_break_frequency` function to find the frequency of chains being broken in a sample set
* `find_clique_embedding` function for pegasus
* Exceptions for specific embedding issues in `dwave.embedding.exceptions`

Bug Fixes
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* `EmbeddingComposite` embeds in spin-space, eliminating some energy range errors.

- Add `LazyFixedEmbeddingComposite`
- Use feature-based solver definition in `DWaveSampler`

* New `dwave.embedding` subpackage