Refactoring of the print sub-system and API clean up.

1. Now a user state has ins own spooler since the spooler app is
   running per user. The user state registers an observer for the state
   of the spooler to get information needed to orchestrate unbinding
   from print serivces that have no work and eventually unbinding from
   the spooler when all no service has any work.

2. Abstracted a remote print service from the perspective of the system
   in a class that is transparently managing binding and unbinding to
   the remote instance.

3. Abstracted the remote print spooler to transparently manage binding
   and unbinding to the remote instance when there is work and when
   there is no work, respectively.

4. Cleaned up the print document adapter (ex-PrintAdapter) APIs to
   enable implementing the all callbacks on a thread of choice. If
   the document is really small, using the main thread makes sense.

   Now if an app that does not need the UI state to layout the printed
   content, it can schedule all the work for allocating resources, laying
   out, writing, and releasing resources on a dedicated thread.

5. Added info class for the printed document that is now propagated
   the the print services. A print service gets an instance of a
   new document class that encapsulates the document info and a method
   to access the document's data.

6. Added APIs for describing the type of a document to the new document
   info class. This allows a print service to do smarts based on the
   doc type. For now we have only photo and document types.

7. Renamed the systemReady method for system services that implement
   it with different semantics to systemRunning. Such methods assume
   the the service can run third-party code which is not the same as
   systemReady.

8. Cleaned up the print job configuration activity.

9. Sigh... code clean up here and there. Factoring out classes to
   improve readability.

Change-Id: I637ba28412793166cbf519273fdf022241159a92