Improvements to the cursor accuracy

From now on the cursor will select the closest object around when it is not directly above an object. The goal is that small objects can be more easily selected from a far away distance. It should also be easier to select objects that are around a pile of objects.

If you only see a few pixels of an object, it will still be necessary in several cases that you remove the object above it in order to take the one under.

Let us know how it feel.