Implement AutoEncoder interface with Lasagne backend.

[alexjc]

This was previously provided by PyLearn2 but removed since the library is no longer maintained. A Lasagne implementation that supports convolution too would be great!

[alexjc]

Lasagne/Lasagne#392

[sumanyu]

@alexjc Is the PR for Lasange's backend impl still pending? I was trying to follow the advanced section http://scikit-neuralnetwork.readthedocs.org/en/latest/guide_advanced.html but hit no backend sub-module imported error.

[alexjc]

The ae part is not implemented yet, no. Help welcome until I can find some time...