Fixed compilation error caused by the previous changes, and changed to use pointers to SimulationInfo in Network and Simulator classes.

Fixed compilation error on 'Refactored size variable to be private’.
Now Network class and Simulator class have pointers to SimulationInfo
instead of local copy of them so that the system maintains a single
instance of it.
Initialize Vm using Vinit at LIFSingleThreadedModel::updateNeuron
Eliminated deltaT from AllNeurons and AllSynapses

Eliminated deltaT from AllNeurons and AllSynapses, and referred deltaT
in SimulationInfo instead.
Renamed the function name updateNeuron() to initNeuronConstsFromParamValues()