Add hoverinfo skip

[john-soklaski]

Add a new hoverinfo flag 'skip'. This prevents a trace from being considered for hovering or clicking. Addresses #678.

[john-soklaski]

@etpinard I'm working on testing gl2d and gl3d plots

[john-soklaski]

@etpinard I was able to add some support for gl2d and gl3d.

There are a few limitations that I'm aware of: because gl2d and gl3d use the gl-plot2d and gl-plot3d packages for picking, traces with hoverinfo: 'skip' still affect the picking logic. I was able to prevent the spikes from being shown for the gl2d plot, but gl-plot3d handles the spikes drawing internally.

[etpinard]

I was able to prevent the spikes from being shown for the gl2d plot, but gl-plot3d handles the spikes drawing internally.

Spikes in gl3d plots are controlled via the layout.scene.?axis.showspikes options. They are effectively decoupled from the hover logic. See how the first modebar button from the right toggles showspikes here. In brief, you don't have to worry about the 3D spikes.

Regarding gl3d and gl2d, I was most concerned about making sure that 'skip' does as good as 'none' at this stage. I don't mind if 'skip' only works for plots that pass through Fx.hover.

Great. So looks like you got everything right. Thanks for adding those tests!

The only thing missing is adding information about 'skip' vs 'none' in the hoverinfo attribute declaration description field.

I'll take this PR for a final spin on Monday, before merging. Thanks again for you efforts.

[john-soklaski]

@etpinard Thanks for taking a look, I've added some information to the description about the behavior of skip and none.

[etpinard]

Great. Thanks!

[etpinard]

Great PR. @john-soklaski thanks very much for your efforts 🎉