Changes for 2.2.20

• Improved LinkingTool.doActivate to assign the location of the LinkingBaseTool.temporaryToNode (or the LinkingBaseTool.temporaryFromNode, if drawing a link in the reverse direction) so as to avoid momentarily seeing where the temporary node had been the last time the user tried to draw a new link.
• Corrected functionality when a browser cancels a Pointer event (for instance when the browser is minimized during ongoing Pointer events).
• Corrected GraphObject.mouseLeave sometimes not getting called when the user's pointer leaves the Diagram.
• Fixed iOS Safari text highlighting when dragging Pointer events out of a Diagram.
• Fixed a regression from 2.2.18 where link JumpOvers might cause "Change not within a transaction" warnings on model load.