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 in the case of a NFC keyboard that is available in the market. Unit test only tests if handleEvent "reset-screen-idle-timer" has been called in ScreenManager.