Support for GNN specific Normalisation Layers

[achiverram28]

There are GNN specific normalisations which play a crucial role in Deeper GNNs, or help in overcoming oversmoothing. There arises a necessity to implement these in order to enhance the Deeper GNNs .

Listing a few important GNN normalisation functionalities / layers here . Will be constantly updating it

• [ ] PairNorm
• [ ] GraphNorm

I will be working on the implementation of these and will make a PR on it and add more useful normalisations here