Make the PredictionIO scala SDK independent from Play!

[filosganga]

Because of:
playframework/playframework#2235

Most of the code in this plugin can be externalized to use as separate PredictionIO scala SDK.

The above issue is currently marked a closed but it isn't because the play-ws is a separate module, but still depends by playframework and ningWS plugin.

So this is blocked by that play issue, but it something is going to be unblocked, at some point.