Plumbing for screen pinning request from sysui

Removes lock-to-app request dialog from the AM.

Added a showScreenPinningRequest to IStatusBar to handle the
flow from app requesting lock task to showing the dialog.

This CL also allows startLockTaskOnCurrent (system|signature) to
start lock task directly.  (Note: this is the less locked version
that always allows exit through back + recents)

Bug: 16957435
Change-Id: I284918dd5989de6cb2767c2a717529eb5e9c6db4
diff --git a/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java b/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java
index c28e0bc..58c3ea1 100644
--- a/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java
+++ b/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java
@@ -23,4 +23,5 @@
     void buzzBeepBlinked();
     void notificationLightPulse(int argb, int onMillis, int offMillis);
     void notificationLightOff();
+    void showScreenPinningRequest();
 }