support ordinal y scale for bubble/scatter plots

[gordonwoodhull]

While it has special cases for an ordinal X scale, currently coordinateGridMixin assumes that the Y scale is linear. This doesn't always makes sense for bubble or scatter plots.

Here is a fiddle sort of halfway hacking around the problem in prepareYAxis:
http://jsfiddle.net/gordonwoodhull/xZFx4/10/

[the3ver]

At least for a scatter plot I was able to get a simple example running with both x and y scales ordinal:
http://jsfiddle.net/the3ver/Lf72gmmy/3/

Looks like the prepareYAxis workaround is no longer necessary.

This also works in a seriesChart version:
http://jsfiddle.net/the3ver/Ldzn11u1/1/

@gordonwoodhull although the above examples work, when i add

.renderHorizontalGridLines(true)

I get

TypeError: scale.ticks is undefined
_dc/dc.coordinateGridMixin/_chart._renderHorizontalGridLinesForAxis  coordinate-grid-mixin.js:699:44

Should this go into a new issue? I was able to fix it and can provide a PR.

[gordonwoodhull]

I see.. probably because d3.scaleBand is its own thing now, instead of having to calld3.scale.ordinal.rangeBands

[gordonwoodhull]

This is fixed by using d3v4 in dc.js 3.0, except for the ticks undefined problem, which is fixed by #1448.