Image browser : moving transformations up and down a branch using the mouse

[pierrelabreche]

It would be convenient to let the user arrange transformations along a branch by dragging the mouse.

[jsachs]

Moving transformations to other locations in the image tree can fail in a number of complicated cases due to circular references and other issues. Sometimes copying a transformation is OK but deleting the old one has consequences. For this reason, I did not try to implement drag and drop and went with the select and copy metaphor instead. A lot of checking for potential errors goes on when you click the copy button and this method also lets you multiple transformations at once which would also be problematical using drag and drop.