Keyguard: Ensure that a widget and page is attached before attaching the ChallengeLayout.OnBouncerStateChangedListener

otherwise it can result in a NPE due that the page was not loaded. Especially on low end
devices this can happen (see zoomOutToBouncer() method @KeyguardWidgetPager)

Change-Id: I7e940eb2fdf885f158f4c5ff2872ebafcda76da0
Revert "FW: Menu & home unlock [1/2]"

This reverts commit 45312dc2e2a1798c03124636fce5b3a8e5261a81.
[1/2] FB: Make menu unlock configurable

For devices with hardware menu keys, menu unlock is turned on by default
This can cause unintentional unlocks. This commit adds the ability to turn
Menu Unlock on or off as desired (Settings -> Security)

System Default is for menu unlock to be ON. This default value can be
overriden using a device overlay:

overlay/frameworks/base/packages/Keyguard/res/values/config.xml
<!-- Allow the menu hard key to be disabled in LockScreen on some devices -->
    <bool name="config_disableMenuKeyInLockScreen">true</bool>

This commit requires the matching commit from Settings repo:
https://gerrit.slimroms.net/#/c/2395/

Based On: https://gerrit.omnirom.org/#/c/3317/

PS6: correct config/overlay location and make multiuser compatible
PS7: derp
PS8: remove the symbol
PS12: rebase

Conflicts:
	core/java/android/provider/Settings.java

Change-Id: I3b6108e4bd403cb76827daed226a4d6a5b868741