Sankey hover text placement

[jackparmer]

@alexcjohnson noticed a hover placement issue with Sankey - here the 633 appears on top of the white box instead of inside it. Not sure if it's a JSON construction issue or a Plotly.js issue.

The wapo hover text can also go off into the ether and does not always seem to point at the selected line:

Both of these examples are from https://medium.com/@plotlygraphs/4-interactive-sankey-diagram-made-in-python-3057b9ee8616

/cc @monfera @alishobeiri

[monfera]

This codepen example also has links both with and without label, and both render fine:

I'll look at how the data is different here.

[monfera]

Reopening to be able to link the other fix (closing only when that's done too)

[monfera]

@alexcjohnson the only remaining problem is the sometimes misplaced tooltip, seen when the browser window here is wide and div.svg-container gets a margin: auto, as inlined style. Any quick thought on where this auto is coming from? I copied data and layout and I didn't get that. I can look it up if it'd take time.

[monfera]

Added an effective fix, and, depending on the answer I'd need to add an appropriate test. It looks like our guideline on fluid layout tampers with the gd margin rather than the paperdiv (=== div.svg-container) margin.

[monfera]

With the above last PR (thanks @alexcjohnson for the review) I think the two problems reported in this issue, and a third one I ran into (node became invisible if value was comparatively low), and a fourth one surfaced by the preceding item (reworking node/link pixel alignment as the small mismatch looked off when the node was very small) are taken care of and merged into master.

[monfera]

As discussed with @alexcjohnson we're closing these issues as fixed by the linked four PRs.