Framework: Clean up / Refactor Mount APIs

 - Move android.storage.* -> android.os.storage.* and refactor users
 - Refactor generic shares back to explicit ums enable/disable/isEnabled
 - Remove media insert/removed event callbacks (not ready for Froyo)
 - Remove 'label' from volume state change callbacks
 - Add public API functions for enabling/disabling USB mass storage (permissions enforced
   in MountSevice)
 - Remove some stray un-needed import lines
 - Move android.os.IMountService / android.os.IMountServiceListener -> android.os.storage
 - Improve code comments

Updated:
  MountService: Add dup state check and move debugging behind a conditional
  UsbStorageActivity: Fix review comments + a TODO
  StorageNotification: Add @Override tags
  StorageManager: Don't use a static Listener list
  MountService: Reduce bloat and fix == where I meant .equals()
  PackageManagerTests: Update for new API

Signed-off-by: San Mehat <san@google.com>