data model options

@Dwaynekj Hey DJ, While refining/updating issue #614 (v3 prep), I came across your change to the calling signature of the data source constructor, which I’m sure you recall was in support of group view's tree column.

You added two parameters to the constructor. While pertinent to the current “standard” datamodel, it is meaningless to a generic “black box” datamodel, which should not need to support those parameters.

I propose changing it to a generic options object. I'll post a PR.

cc:@dcchuck