Add NeuroMLlite version of spiking network

[pgleeson]

@ronaldonunes Have a look at this file for an example using NoisyCurrentSource: https://github.com/OpenSourceBrain/StochasticityShowcase/blob/master/NeuroML2/nmllite/NoisyExample.py

It works with:

python NoisyExample.py -jnml    
nmllite-ui SimNoisyExample.json 

but just tested with jnml so far. Working on getting it mapped nmllite -> pynn.