Add keep device from sleeping permission

It gets annoying to shop while holding the devices and have the device keep going to sleep particularly if there is a device lock in place.  We need to be able to optionally specify the app should keep the device awake or at least extend the sleep/screen off interval temporarily while the app is opened.  It should still dim the screen to next to nothing during idle but never require a full device unlock to get going again during a shopping trip.

This suggestion goes hand in hand with the suggestion for more deliberate check-off items on lists in order to help prevent unwanted or accidental check-offs.