#78 Problem moving OOBN instance node

[Rommel Novaes Carvalho]

When we instantiate a OOBN class (create a node instance of frame), the frame is created having its center point being where the cursor is, i.e., when we create a node with the mouse on the left upper corner, half of the node is outside of boundaries.

As the only part allowed to be used for moving the node arround (for frames) is the label in its top, these nodes created with half outside the boundaries can never be moved again, since the scroll cannot go to negative coordinates.

This was not a problem on the previous GUI, because we could use any part of the frame to move it around. However, this became a problem on the new GUI.