Update OBB API to include callbacks

Add a callback for users of the StorageManager API to be able to receive
notifications when the requested operation completes for mountObb and
unmountObb.

Add NDK API to get to ObbInfo like the Java API has.

Also update the docs for the API and remove the "STOPSHIP" comments.

Change-Id: I23a4409c7f8b74d3169614beba920b4d667990a4
diff --git a/native/android/Android.mk b/native/android/Android.mk
index cc35a3a..44ec83f 100644
--- a/native/android/Android.mk
+++ b/native/android/Android.mk
@@ -12,6 +12,7 @@
     looper.cpp \
     native_activity.cpp \
     native_window.cpp \
+    obb.cpp \
     sensor.cpp \
     storage_manager.cpp