When using an Ogre picker on a medical image, the picked position does not correspond to a voxel position of the image. In fact, the Ogre negato display the image between [0;size] and the picker needs to pick between [0;size[.
This MR adds a new picker to realy pick the image current slice.
Closes #616 (closed)
How to test it?
Tuto11Picker with an image and check the picked depth value, it must be the image spacing multiply by the current slice index.