Added RBM functionality.
Added a class for using RBM specifically.
Forced UpDown inference for RBM.
Added reconstruction_cost to DBM monitor.
Fixed history output for UpDown.  I didn't really understand the fix, but UpDown was outputting one more history element than WeightDoubling.  So I removed the first element from the output.
Modified dbm_demo/rbm.yaml to use RBM class.  Modified learning rate slightly.  Features *look* good and the reconstruction cost goes down for several epochs.  Need to add further tests.