Reworks lock screen flows.

This also adds frp warning dialogs in case the user skips lock
screen setup initially.

bug:26880444
Change-Id: I732b6a806e139fb6c1c1b334b8d1608c229f217c

proguard.flags

@@ -22,3 +22,7 @@
 -keepclassmembers class com.android.settings.inputmethod.UserDictionaryAddWordActivity {
   *** onClick*(...);
 }
+
+-keep public class * extends com.android.setupwizardlib.items.ItemHierarchy {
+    public <init>(android.content.Context, android.util.AttributeSet);
+}