Show educational tooltip for incomplete ways and nodes

[claudiush]

Currently users - in particularly new ones - need to discover and memorize the color coding for both ways and nodes to understand what element is currently missing. E.g. a yellow way is lacking the lanes attribute. This would help to reduce onboarding time to this tool even further on the expense of relying more on text (and localization) instead of pure visual through colors and symbols.

SVG path elements would allow for tooltips like functionality (following is a mockup)

...through the title tag, e.g.
<path class="leaflet-interactive" stroke="orange" stroke-opacity="0.7" stroke-width="6" stroke-linecap="round" stroke-linejoin="round" fill="none" d="M963 -1197L950 -1244">
<title>Lanes attribute missing</title>
</path>
...unfortunately Leaflet's Polyline class currently doesn't expose such option yet: http://leafletjs.com/reference-1.0.3.html#polyline

There's a feature request to add it though: Leaflet/Leaflet#4179

[k1wiosm]

I will think about it.