Bug 975268: [System][NFC] Reset the screen idle timout when a NFC tag/device is detected

This bug adds a way to reset the idle timeout when NFC detects the presence or the loss of presence, of a tag or device.

It does not wakelock the screen, as that is a good way to drain a battery. Unit test only tests the callback has been called in ScreenManager.

Rebase when Bug 963556 lands.