Avoid trees to close to buildings and footways

[Matthias84]

Places like zoos, theme parks or cementories are usually covered with a lot of trees. Most areas just add a nature=wood to charackterize this land cover. Unfortunatly this seems to result in a pretty dense filling with trees, which touches buildings but also the ways like here at the Zoo Rostock

Maybe you could add a test, if a tree comes to close to buildings or streets / footways? Yes sometimes this objects are covered by a tree, but usually not that much?

[ivanbranco]

Related issue: #49