Fix double-clicks for copying in Edit Position mode

Fix double-clicks for copying in Edit Position mode

The time measurement between clicks on the same square in Edit Position
mode was seeing presses as well as releases, so that a fast click would
be mistaken for a double click on that square. Only presses should be
judged this way. In addition the piece should be grabbed for dragging
again on the second press, as the first release had ended the drag.