Offload database handling to seperate thread

While debugging, I realised that the onResponse method used by Volley is called on the main thread.
 This is good for some/most situations but not here were we use loaders to monitor the database,
  reporting changes on the main thread. Since we do not need access to the UI from the response
  listener at all we can use a simple Java Thread here. A basic cancellation method has been provided.

Change-Id: Ibf8f1390da5d6862561ba8735b7bf4fd7735edff