Go-Through boxes

When the player or a box is clicked the reachable squares are now shown with a little circle graphic.
The player can now "go through" boxes that can be pushed away and then back to the original position for reaching the actual box to be pushed.

Example:

A white circle indicates reachable positions that can be reached without the go through feature.

A dark square indicates positions that are only reachable when pushing boxes due to the go through feature.

The boxes that can be used to "go through" are marked with a black circle.

Using this feature it's possible to select a box for pushing that can only be pushed when going through other boxes by pushing them first away and the back to the original position.