Now storing all necessary data from forward prop
    * Activations replaced with PropData
        * Stores signal at each stage, for each layer
            * after summing, after activating, after filtering
    * Activator/Filter/Weights
        * Changed propogate to properly store PropData
    * Newtypes
        * Moved Update to Propogation
PropData fix
    * Should be tracking the signal *before* each transformation,
      not after
    * Propogation.hs
        * Changed lens & field names to reflect the above
    * {Activator,Weights,Filter}
        * Changed propogate implementations to reflect the above
    * NeuralNet.hs
        * Corrected propogate to reverse layers first
Monadic backpropogation
    * Reads the PropData from propogate, writes [Update]
    * Implementations added to all Propogate instances