Plot Fixes (Qwt 6.1.2 upgrade): Printing: Line Thickness and Background Colors
Bug Number: n/a
Release notes (y/n): no
For Release Nums: 6.8

This commit fixes two problems introduced with RiverWare's upgrade from 
Qwt 5.2.3 to Qwt 6.1.2. 

  (1) The printed backgrounds (both inside the canvas, and in the axis/title 
      area) are grey. They should be white.
     
  (2) The "Plot Mode Line Width Factor" -- which increases the width of lines 
      in Print Output (both to paper and to PDF) -- needs to be significantly 
      reduced, with a default of 1 (instead of 12).  Qwt 6.1 now does a 
      better job of adjusting line thicknesses for super-high resolution 
      graphics "devices", such as printer output.

More Technical Information:

(1) Printed Backgrounds. In the following three methods, we now explicitly, 
temporarily, set both the SlotPlot's (QWidget's) Background Palette Color and 
its (QwtPlot's) Canvas  Background Color to white.  One of these three 
methods supports the creation of images for plot pages in model reports 
(which has also been tested).

  (a) void PlotDialog::paintPlots (QPainter* ...)
  (b) QPixmap PlotDialog::renderPlot(int plotNum, QSize pmapSize);
  (c) void SlotPlot::paintPrinter (QPrinter*, ...)

(2) The upgrade from Qwt 5.2 to Qwt 6.1 changed the behavior of "plotting" 
to super-high resolution graphics devices -- such as printers.  Qwt 6.1 now 
does a better job of adjusting line thicknesses for super-high res.  This is 
still heuristic, and it does make sense to still provide an adjustment for 
special presentation uses.  But a better default for the Print Line Width 
Factor is now 1, instead of 12. See this image:

    http://cadswes2.colorado.edu/~philw/2015/Qwt/Printing/PrintLineWidthFactor.png 

The RiverWare 6.7 Technical Documentation (Output.pdf, page 22) includes 
this paragraph:

    The Print Line Width Factor is used to specify how wide you would like 
    printed lines on paper or PDFs. During printing, all of the slot curves' 
    and markers' line widths are increased using a function of this factor. 
    Typical values are 10-20 and the default is 12. 

Draft change [Phil]:

    The Print Line Width Factor, normally 1, can be increased to increase 
    the thickness of slot curves and marker lines, by this multiplicative 
    factor, when printing plots to paper or PDF files. 

The Print Line Width Factor default has been changed (from 12 to 1) AND the 
QSettings (Windows Registry) symbol has been changed so that any previously 
saved value is replaced with the new default.  See this RegEdit screenshot:

    http://cadswes2.colorado.edu/~philw/2015/Qwt/Printing/QSetting-PrintModeLineWidthFact2.png
    Old Symbol: printModeLineWidthFactor
    New Symbol: printModeLineWidthFact2

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