Add scaffold for sparse auto-encoder.
Visualize auto-encoder.
Add sparsity to fully connected layer.

That does not work yet.
Revert "Add sparsity to fully connected layer."

This reverts commit 84c69e6b6b7c0a2010909a5c972dd2fc165c3bde.
Use sparsity constraint.
Accelerate visualization.
Tune some parameters.
Add LBFGS scaffold.
Fill LBFGS scaffold.
Move L-BFGS implementation to .cpp.
Add LBFGS to python bindings.
LBFGS is not CG.
We now have L-BFGS.
SAE does not inherit from Net any longer.
Rough implementation of SAE.
Some fixes.
Use less instances for debugging.
Fix some bugs.
Add test case for SAE.
Add biases.