Allow manual specification of region ID. Added test for region ordering.
Use SDRAM size for DTCM unless the vertex has a dtcm_usage attribute.
Allow each vertex to write its own runtime to memory.
Set the runtime on each vertex prior to partitioning.
Merge branch 'refactored-vertices3' into spike-recs
Allow unwritten regions to go through as unfilled.
EnsembleVertex creates a RECORD region and leaves it unfilled.
Add method to retrieve region data from SpiNNaker.
[Bugfix] Copy to `_sdram_current` not `&_sdram_current`
Allow edge functions to specify either only a pre- or a post- type object.
Remove buffer->record override.
EnsembleVertices can start recording.
(Spike) probing completed.

- Probes are created by the Builder as required and given to the simulator.
- At the end of simulation the Simulator asks the Probes for their data and
  stores the result.
- Probes manage retrieving data from SpiNNaker and formatting it as required.