Data cursors for figure window

Data cursor support for multiple axes in a fugure

Several related functions:

CreateCursor sets up a vertical cursor on all axes in a figure. The cursors can be moved around using the mouse.
Multiple cursors are supported in each figure

GetCursorLocation returns the location of a cursor while SetCursorLocation sets it.

DeleteCursor removes a cursor.

Objects belonging to each cursor have their handles stored in the figure application data area. Callbacks for each object serve to link their position on the axes.