Packaging Improvements

In Developer installs (i.e., from `git clone`) running `make all` in `spinnaker_components` will copy the output binaries to `nengo_spinnaker/binaries`.  `setup.py` looks for binaries (`*.aplx`) in this location and will incorporate them into built `sdist`s.

Vertices will now look for their binaries in either the developer install environment, or in the system install environment.  In the case that package was installed as an egg, and setuptools is installed, the binaries will be extracted on demand.

As a user, given an `sdist` it is possible to run `python setup.py install` and have everything (including binaries) work.

Some corrections and modifications to `setup.py`.