Add domain argument to GenericTransport (default="all")

[ma-sadeghi]

This would eventually add the ability to properly run simulations on part of the network. For starters, though, we could only return a masked array (interleaved with nans at locations outside the desired domain).

Example use case in PEMFC

Proton conduction in ionomer phase coupled with oxygen diffusion in ionomer + air

Note

Properly supporting this feature (assemble a smaller A matrix, etc.) has performance benefits, for example, running a simulation on half of the network could become ~8 times faster.

[jgostick]

We can add this as a feature in the future, so I have given it the 3+ milestone