Make stepper shutdown after inactivity dependent

Make stepper shutdown after inactivity dependent on a new set of
#defines.
DISABLE_INACTIV_X
DISABLE_INACTIV_Y
DISABLE_INACTIV_Z
DISABLE_INACTIV_E

And make exemplaric Configuration.
Names can be discussed.

This makes the disabling of the steppers independent from the DISABLE_?
settings witch shut down the steppers immediately.