Bulletproof CredentialStorage state handling

As noted by the class javadoc, CredentialStorage has seen the number
of cases to cope with grow. This change tries to address those cases.

	src/com/android/settings/CredentialStorage.java

Added ChooseLockSettingsHelper.EXTRA_KEY_PASSWORD to coordinate
additional producer and consumer.

    constant declaration here, since its used by callers of
    ChooseLockSettingsHelper.launchConfirmationActivity
	src/com/android/settings/ChooseLockSettingsHelper.java

    old producer
	src/com/android/settings/ConfirmLockPassword.java
    new producer (CredentialStorage wants passwords and patterns)
	src/com/android/settings/ConfirmLockPattern.java
    new consumer
	src/com/android/settings/CredentialStorage.java
    old consumer
	src/com/android/settings/CryptKeeperSettings.java

Made class final and removed protected from method to make it clear
ChooseLockSettingsHelper is not to be used by subclassing.

	src/com/android/settings/ChooseLockSettingsHelper.java

Change-Id: Ib2d65398fe44573168a6267a0376c3b0388b16c8