Make time needed for Nao to move to next stroke proportional to distance

[dhood]

Currently there is extra time allowed for the robot to reach the first point on a message because it probably has to lift its arm from the rest position. In message_echoer, there may be multiple strokes published in succession, and the robot may not actually need this extra time because its arm is already lifted. The time allowed to get to the first point should be based on the distance the robot has to move to get to it. Or, better yet, the robot should move to the first point as fast as it can, and notify the tablet when it's ready to write.