add more Equivariant Layers

[CarloLucibello]

This repo contains a collection of Euclidean Equivariant layers, we can think of implementing some of them

https://github.com/e3nn/e3nn

Some work has been done by @Dsantra92 in https://github.com/Dsantra92/e3nn.jl Maybe we can incorporate that in the main library here