Quadindex refinement

This is needed for the feature_tree search (and the all-in-one search) to work problery on all zoom levels inside RE3.

Searching with a bounding box using quadindex works great. But there was one problem: if the passed bounding box was bigger than the `'0'` bounding box of the quadindex, the mortonkeyspace could not be created and thus no results could ever be found for such bounding boxes (even though the whole of Switzerland was inside the bounding box).

This PR assures to reduce the passed bounding box to the `'0'` bounding box of the quadindex by intersection.

Note that a passed bounding box which is completely outside of the `'0'` still fails, which is as we want it.