Different icons based on query result

[JeroenDeDauw]

Requested by @c-ern at SemanticMediaWiki/SemanticMaps#24

In order to being able to distinguish each query result displayed on a map it would be great if each one was shown with the according icon.
I.e. one would search for fast food restaurants in a town, the location of McD would be displayed with its signature golden M, BK with its logo and so on.
One possibility to implement this would be to add a new attribute like "has custom_marker=mcd.png" to the corresponding page and add this ?has custom_marker to the ask-query.