Restore feature compatibility with QPrinter in QTextDocument::print

Restore feature compatibility with QPrinter in QTextDocument::print

Add a margin method to QPagedPaintDevice. The other variables
required are stored in QPagedPaintDevicePrivate without a
public API for now. This needs cleaning up once we have a new
printing system.

Change-Id: Id3f2d7ac7f3cbce8619072a897d91f3a588add64
Reviewed-on: http://codereview.qt.nokia.com/3211
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@nokia.com>