Hover & text on shapes

[nicolaskruchten]

We don't want layout shapes to be full traces but it would be pretty convenient to be able to add hoverlabels and text to them, for something like object-annotation or to label horizontal lines on plots.

[jorgenherje]

@nicolaskruchten Would be nice with hover text for shapes.

Shapes are nice to utilize for marking/annotation in plots with vertical/horizontal lines. However it would be nice to have hover text, s.t. info is not visible at all times.

Working in WebViz using Dash and plotly. I've been testing some ways to obtain vertical lines with text info, and found the two possible solutions so far:

1. Shapes + annotations (text labels always visible - not optimal):
   

2. Vertical trace (must add after data, and calculate min and max y-value. Can become slow with many traces? And does not span across y-axis when zooming out):
   

[RichardNeill]

Agree, this would be great. If we can't have the full "hover" mechanism, what about enabling
the HTML title attribute?