Addresses the following:
- Rename nnconv5 block to nnconv5
- Add skip connections directly to nnconv5 block
- Allow custom metrics, loss and optimizer (keep defaults that reflect original paper) to train
- Correctly use nyu evaluation dataset only when no dataset is provided
Found from DenseDepth, each layer can be set to trainable in the encoder, then the outputs of the
model and the required layers for skip connections can be used directly. Ends up being much cleaner