Add tourstop pin for tours that intersect current node

[lentinj]

Add tourstop pin icon to leaf nodes that are part of a tour. Approximately above the (C) image copyright button

Use this to open a "Tours" tab in in the node pop-up, listing all tours available at this point.

[lentinj]

@jrosindell Whilst continuing to wrestle with this, I've noticed that we currently say "you could sponsor this leaf" for unavailable leaves, e.g. human. There's nothing we can immediately do about this, since the client doesn't know about the unavailability, unless we mine this information out.

However, a simpler solution could be to make the "unavailable" page be a general donation page. Then there's no need to attempt to hide the link in these cases.

(this should be a separate issue if this is something we want to do)

[lentinj]

The data side of this is done, the visual appearance is going to be dealt with at some other stage.