Implement continuous tape labels and path-based label shapes.

- Added "roll" as a special paper id
- Added roll_width attribute to draw tape in previews
- Updated Brother QL-500/* label templates
- Preserve print dialog settings between print jobs.
- Added path based labels for arbitrary shaped labels.
- Fleshed out implementation of continuous labels.

model/StrUtil.cpp

@@ -61,7 +61,7 @@ namespace glabels
 				if ( denom[i] == 0.0 )
 				{
 					/* None of our denominators work. */
-					return QString().sprintf( "%.5g", x );
+					return QString().sprintf( "%.3f", x );
 				}
 				if ( denom[i] == 1.0 )
 				{