[Bugfix] Remedy for Dual Axis chart render bug

[Mogball]

An attempt to remedy #4115, which seems to be the result of issues handling annotations for Dual Axis Line Charts.

The first issue is that the most recent nvd3 release 1.8.6 does not expose xScale (although it exists in nvd3/master), and secondly there is yAxis1 and yAxis2 instead of just yAxis.

Making up for xScale isn't an issue because multiChart just uses d3.scale.linear() but I'm wondering how annotations are handled for two axes? @fabianmenges

[kkalyan]

thanks @Mogball, this fixed #4115.

[fabianmenges]

Right now, annotations are not supported with the Dual Axis Line Chart slices (in the sense that I have not tested and developed with them in mind and I'm pretty sure they are not available through the UI).

@Mogball Your fix looks good, but there are probably some other things that need to be hooked up, for it to actually work e.g.: https://github.com/apache/incubator-superset/blob/master/superset/assets/javascripts/modules/AnnotationTypes.js#L59

@kkalyan did you setup annotations in a time series 'single'-line chart and then switch over to dual line chart? We probably need to add some code that wipes/ignores annotations if the current slice/chart type does not support the type of annotation configured.

[Mogball]

I seemed to have been getting the same errors even though I didn't create any annotation layers.

[mistercrunch]

Lacking the whole context, should I merge this?

[fabianmenges]

This is a bug, we should merge it.

[fabianmenges]

@Mogball you are right, this is an issue even when no annotations are selected.