Use defaults to find parameter_names

[Christian-B]

As we are moving to using spynnaker/pyNN/models/defaults.py for all models

Why not have that class also discover the data needed for
AbstractHasParameterNames.get_parameter_names

This will avoid issue like in

sPyNNaker/spynnaker/pyNN/models/neuron/plasticity/stdp/timing_dependence/timing_dependence_vogels_2011.py

Line 46 in 64d0914

__PARAM_NAMES = ('alpha', 'tau')

Where some params are included and others are not