Work on using Timer2 for output.

- Stripped interleaved output out of neuron update.
- Added new output function.
- Added calculation for delay between output packets.
Merge pull request #6 from ctn-waterloo/ensemble-tx-smeared

Regularised output for Ensembles using Timer 2
Tracking changes made by @tcstewar
Explicity added vertex attribute to EnsembleData for my sanity.
Include constant Nodes in the bias of their receiving Ensembles in encoded form.  This fails to include filtering.
Merge pull request #7 from ctn-waterloo/constant-node

Constant Nodes
Safer check for constant nodes.
Test files to watch for udp packets
Changed port
Fixed length of message bug
Actually run the model for 10 seconds
First pass at handling SpiNNaker->PC message passing
Example to test transmission from SpiNNaker to host
Added handling to pass received data from SpiNNaker into Nodes
Merge branch 'tx-to-pc' of https://github.com/ctn-waterloo/nengo_spinnaker into tx-to-pc