[2/2] Settings: 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 frameworks_bases repo:
https://gerrit.slimroms.net/#/c/2394/

Based on: https://gerrit.omnirom.org/#/c/3318/

PS7: update overlay location
PS8: fix config value retrieval
PS9: rebase
PS10: catch NPE of mMenuUnlock if screen lock 'pattern' is used

Conflicts:
	res/values/slim_strings.xml

Change-Id: I8fc38b17315a050b10bb6d5fb13f6abf0f306e08

Conflicts:
	res/xml/security_settings_chooser.xml
	src/com/android/settings/SecuritySettings.java