JS: add method isFinished to Device
JS: add method isFinished to Device

This method will be made abstract once its overrides are in place.

Signed-off-by: Harry King <409587b9e6671aa0763646191d292852dc49a658@gmail.com>

jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim