Labels/Titles/Tooltip for spitsgids occupancy icons

[SerkanYildiz]

After the release of iRail with Spitsgids integration in it, I got some feedback like, what do the icons mean. Maybe we should add some title/tooltip for the image tags. But I don't know what the best practice is for mobile devices. @xavez do you have an idea?
Link to feedback on Twitter; https://twitter.com/Smienos/status/758689130666655744

[xavez]

That's a hard one. Because it is so tied together with the system we select: will we keep three levels of occupancy? How about smiley faces: :) and :(. Or how about no icons, just text? Many options to be explored. Ideally, we have Arne's input here as well, because how we presented is so tied together to what we want to measure.