Add topology_utils

[mahdiehmalekian]

The added files in dwave/graphs/generators/common provide blueprint classes for working with different aspects of any D-Wave topology.

• coord.py: Coordinate systems used for node labels.
• node_edge.py: Nodes and edges.
• planeshift.py: Displacement of nodes in the Cartesian plane.
• shape.py: Shape of a graph.
• topology.py: Constructing a topology graph whose nodes and edges are equipped with all the specific-topology-relevant functionalities.

The added files in dwave/graphs/generators/zephyr, i.e. zcoord.py, znode_edge.py, zplaneshift.py and zshape.py, contain the implementation of the corresponding objects for Zephyr topology. In zephyr.py the class Zephyr has been added that is built on Topology blueprint in dwave/graphs/generators/common/topology.py

In dwave/graphs:

• tuplelike.py is a helper for working with various objects which can be uniquely identified with a small set of values.

The test suite for these modules is added in tests.

Note: This is an evolution of previous zephyr_utils PR to minorminer.