tmf: add minimum margin for right mouse drag zoom

tmf: add minimum margin for right mouse drag zoom

This will prevent zooming when the right drag is less than 5 pixels.
For extensions that define a context sensitive menu for time events,
this will prevent zooming when the user accidentally moves the mouse
when wanting to get the context sensitive menu.

Change-Id: I198aaac1212f2f762e1dbe87d3fa3cb115a5d3a5
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/79370
Reviewed-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-by: Jean-Christian Kouame <jean-christian.kouame@ericsson.com>
Tested-by: Jean-Christian Kouame <jean-christian.kouame@ericsson.com>