#185 current.cursorPosition duplicated in code

[Fogh]

Current has both current.position / positions and current.cursorPosition

current.position is apparently never used, set in only one place (in Viewbox.mouseClickEvent), and identical to current.cursorPosition. We shoudl get rid of one of these, to avoid future confusion, but it does need an OK, in case it might generate bugs.

[wb104]

current.positions is the last clicked location.
current.cursorPosition is the last "hovered" position.
(Note there the former has an "s" and the latter does not.)
We don't use the last clicked location for anything so could get rid of current.positions.