Add LocalNet

[kate-sann5100]

Is your feature request related to a problem? Please describe.
LocalNet, which is a common image registration network is not available in current package.

Describe the solution you'd like
Implement LocalNet.

Describe alternatives you've considered
N/A

Additional context
DeepReg implementation of LocalNet
Reference:
Weakly-supervised convolutional neural networks for multimodal image registration.
Label-driven weakly-supervised learning for multimodal deformable image registration