Anomaly parameters exposed from OPF/swarming

This change allows us to set anomaly params in OPF description file (and thus swarm over them), eg: 
` 'anomalyParams': {
       'mode': 'pure', # pure(=default) / weighted / likelihood
       'slidingWindowSize': 5, # >=0 / None
    },
`

Fixes #1305 
~~Blocked by: https://github.com/numenta/nupic/pull/1353 (builds upon it)~~
Do we need to store the score on the anomaly object? It doesn't look like it gets used anywhere aside from the `__str__` method. I'd say remove it to keep the state to a minimum.