Extrude direct reference

Modified infrastructure code so that Extrude directly references the extruded shapes. Now it has better control over the referenced shape, the tree view structure looks better as the hidden intermediary subshapes disappeared. It seems also to be faster.

This modification was made in order to get better control over the referenced shape solving problems when the target shape needs to be hidden. Ex: when a rectangle is extruded the initial rectangle needs to be hidden.
Will continue fixing bugs higher priority being the Cut and Extrude related ones.