Settings: Move LOCK_BEFORE_UNLOCK to LockSettingsService

This option is now manipulated through LockPatternUtils, which in
invokes the new LockSettingsService instead of the generic
SettingsService (since If9ac2b29e33cd2183fd67af22a8db280c0c6e1a4)

Move this setting there so it passes the in-class filter for
options it's allowed to migrate from CM9, and reject attempts
to change it through the normal SettingsProvider

Change-Id: I628caf92c0f77cbaf759f04b4a396631447b2a11