* Fixed "Cursor Positions on Shared Whiteboards are Inconsistent".

The main fix is in the method cursor_point_to_space in
public/javascripts/spacedeck_whiteboard.js.

The calculation of the coordinates of the mouse pointer from absolute
window to the whiteboard space coordinates was incorrect.

There were a number of dependencies on this method which were updated
as a result.

One side-effect was that the div for the lasso tool needed to be
moved inside the div for the whiteboard.

* Fixed minor panning calculation problem.  Works now!