Use custom tooltip instead of browser tooltip

[thinkh]

At the moment most tooltips are based on Browser tooltips. The problem is that they need a few seconds before they appear. Especially for browsing the diff heatmap it would be helpful if they appear immediatly. Therefore we should replace the browser tooltips with a custom tooltip.

[doomsayer2]

Do you mean like I already did once? With a moving div element? We could use a library too but that would add further code and I dont know how to add a specific library.

[thinkh]

Yes, but everywhere. You can also try a CSS only solution (e.g., https://codepen.io/cbracco/pen/qzukg).