Create graph

[Christian-B]

Builds on #449

An ApplicationGraph is now created during the Writer.setup or mock call. So except for before sim.setup (or unittest_setup())
there is always a graph so no need to call create graph or set_(runtime)_ graph

The Graph Class (or at least what was actually needed) has been merged into ApplicationGraph.
With the following changes

• The Graph no longer has a label so all graph label params removed
• You can no longer set or get constraints on graph (Was totally unused)
• get_edges_ending_at_vertex method removed (no known use)
• add_vertices and add_edges methods removed as only used in tests
• Vertex are now only held as the Values in a dict.
  (This has a minor cost that you can not iterate vertices and add at the same time)
• The allowed Vertex and Edge type to add are now harded coded.

As the Graph is never cloned the clone method has been removed.

As the Graph is never given to the use the ApplicationGraphView is no longer need

Must be done after:
SpiNNakerManchester/SpiNNUtils#184

Must be done at the same time as:
SpiNNakerManchester/SpiNNFrontEndCommon#961
SpiNNakerManchester/sPyNNaker#1202
SpiNNakerManchester/SpiNNakerGraphFrontEnd#217

tested by
http://apollo.cs.man.ac.uk:8080/blue/organizations/jenkins/Integration%20Tests/detail/create_graph/3/pipeline

Documented by
SpiNNakerManchester/SpiNNakerManchester.github.io#42

[andrewgait]

This looks fine to me, just a few minor edits suggested