1. Added support for reporting the old print attributes during layout.
Now we keep track of the old print attributes, so the app can
compute the delta and decide whether re-layout work is needed.
2. Fixed PrintDocumentAdapter callback interleavings. Layout callbacks
were intermixing with write ones - a mess. Now we make an attempt
to cancel layout and write if they respond to cancellation, otherwise
we wait but do not interleave them.
3. Refactored the PrintJobConfigActivity for easier maintenance and
to have a single update UI method that does the minimal amount
of work.
Change-Id: I31ada1a0550882e6185018e6f17f923aed165d15
