Add generic templates (#307)

- Add generic full-page templates.  (This feature from 3.4 was missing)
- Also add generic half-page, quarter-page, and envelope templates.
- Add several more common envelope sizes to page-sizes.xml
- Qt print backend does not need pwg_size.
    - Replace with pwg_class, to distinguish between ISO and NA sizes

model/XmlPaperParser.cpp

@@ -99,9 +99,25 @@ namespace glabels::model
                 Distance width   = XmlUtil::getLengthAttr( node, "width", Distance(0) );
                 Distance height  = XmlUtil::getLengthAttr( node, "height", Distance(0) );
 
-                QString pwgSize = XmlUtil::getStringAttr( node, "pwg_size", "" );
+                QString pwgClass = XmlUtil::getStringAttr( node, "pwg_class", "iso" );
 
-                return Paper( id, name, width, height, pwgSize );
+                Paper::Type type;
+                QString typeString = XmlUtil::getStringAttr( node, "type", "sheet" );
+                if ( typeString == "sheet" )
+                {
+                        type = Paper::SHEET;
+                }
+                else if ( typeString == "envelope" )
+                {
+                        type = Paper::ENVELOPE;
+                }
+                else
+                {
+                        qWarning() << "Warning: unknown paper type: " << typeString << ".";
+                        type = Paper::SHEET;
+                }
+
+                return Paper( id, name, width, height, pwgClass, type );
         }