model parametrization

[ltetrel]

This PR adds a fully dynamic and parametrized GCN model. It suports:

• number of layers (both GCN and fc)
• filters definition (size, number, for both GCN and linear)
• activation function
• normalizations (batch norm and GCN)
• dropout and pooling (edge pooling still not working)

[ltetrel]

Sorry for the mess, I f***** up the merge conflict. git can be really really tricky sometimes...

[htwangtw]

It's okay I am reviewing it today