(1/2) Base: allow to configure the long press back kill delay

defaults to 1000ms (1 second)

Change-Id: I82441d5947940c95ffb62804416f37282a86c54d

Conflicts:
	core/java/android/provider/Settings.java
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java

Conflicts:
	policy/src/com/android/internal/policy/impl/PhoneWindowManager.java