Small fixes
* SpikeSourceArray uses defaultdict and doesn't crash
* v_init works for populations of 1 neuron
More ssa tweaks - use defaultdict
Fix for issue with writing padding longer than 255 entries
proper rounding of weights
Half-finised merge

Merge branch 'origin/master'

Conflicts:
	spynnaker/pyNN/__init__.py
	spynnaker/pyNN/models/abstract_models/abstract_synaptic_manager.py
	spynnaker/pyNN/models/neural_projections/projection_partitioned_edge.py
	spynnaker/pyNN/models/neural_properties/synapse_dynamics/multiplicative_weight_dependence.py
	spynnaker/pyNN/models/neural_properties/synapse_dynamics/pfister_spike_triplet_rule.py
	spynnaker/pyNN/models/neural_properties/synapse_dynamics/plasticity_helpers.py
	spynnaker/pyNN/models/neural_properties/synapse_dynamics/spike_pair_rule.py
	spynnaker/pyNN/models/neural_properties/synapse_dynamics/stdp_mechanism.py
	spynnaker/pyNN/models/neural_properties/synapse_dynamics/synapse_row_io_plastic_weight.py
	spynnaker/pyNN/models/utility_models/command_sender.py
	spynnaker/pyNN/models/utility_models/live_spike_recorder.py
	spynnaker/pyNN/spinnaker.py
Tweaks to STDP, liberal application of @abstractproperty - triplet rule not working, but probably unrelated