Validate step size before send movement command in manual mode

[codiak6335]

When a user changes the step value but fails to hit enter the old value is used for the next movement.

To reproduce:
put cursor in edit window and change the count from 1 to 11, do not hit enter
now move one of the axis by clicking a button.
The machine will move 1mm/in not the 11mm/in...
now move the axis again by clicking a button
This time the axis will move 11mm/in not 1mm/in