Use the Deletion Helper when system storage is low.

A notification is posted when the system storage gets too low.
Currently, it redirects into the Storage Settings. Instead,
it should redirect into the Deletion Helper to directly let the
user clear out their storage.

Bug: 29437277
Change-Id: I4e35adf300d5e479d4171f1e6f090f2a757400f2
6 files changed