change function signature of spades estimator

[briehl]

From

{
    use_defaults: boolean,
    SPAdesParams params
}

to just SPAdesParams.

The idea is that just the parameters used by the app should be used by the estimator. Anything outside of that should be handled by the admins.

[dcchivian]

@briehl @psdehal do you still care about this being pushed through? @qzzhang has some changes in the next PR that she's going to want to test without complication from another code update, so I'd rather we do this PR separately (if it's still desired).

[bio-boris]

@dcchivian We are holding off for the estimator right now, but lets keep the branch around. This way we can deploy this app by a specific commit and test it that way.