Display max_inactive_time and stepper_inactive_time in seconds instead of millis

I changed because it´s more conveniant to set seconds from the LCD menue and IMHO it makes anyway no sense to set the inactive Times in milliseconds.
This would also make a changement necessary in the Repetier host(here is the entity seconds)
Merge pull request #2 from repetier/master

update
Merge pull request #3 from leramleram/patch-3

Patch 3