Anomaly changes

Follow up to #956 by @breznak 

CC @subutai @oxtopus @rhyolight 

WIP!

- [ ] - The current method for specifying the type of anomaly you want doesn't let a 3rd party create their own. Can we change this to a base class defining the interface and then a set of subclasses? Separating into separate classes also makes each method easier to understand and test since you don't have the sliding window logic, etc all in the same class.
- [X] - The anomaly class supports taking either current predicted columns or previously predicted columns. I don't see any reason to have the class support both. Rather than duplicating the previously predicted state I think the new class should take the previously predicted only. (d9ecf61)
- [X] - I don't think we use the KNNAnomalyClassifierRegion but the change there added state to the class with no benefit. It should just use computeRawAnomalyScore. (d5f383b)

Other changes:

- Clean ups (1ad37c0, c8f2af3)
this assignment is unnecessary