Implement remaining operations

[stiber]

Refer to Operations.h. Implement the remaining operations in this order:

• copyFromGPU
• deallocateGPUMemory
• copyToGPU

[stiber]

Includes #130 and #122.

[stiber]

Here's a note from PR 693:

Before this change, registerSpikeHistoryVariable (now registerHistoryVariables) was a member function of AllSpikingNeurons and was called within AllSpikingNeurons::setupVertices().

The main reason for moving this function to the AllVertices base class is to accommodate deserialization. Previously, our flow was setup -> register -> deserialize -> simulate, and recording variables during the setup stage meant missing out on the deserialized vertices.

With this change, the new flow is setup -> deserialize -> register -> simulate, ensuring that all deserialized vertices, are properly recorded.

[stiber]

Also, need to incorporate things done collectively by Simulator::setup(), Model::sertupSim(), Layout::setup(), Vertices:: setupVertices(), etc., and their subclasses.