Fix selection of fonts based on styleName

By carrying the styleName through from QFontDef to
bestFoundry and giving it to bestStyle that can use it
we can accurately match fonts based on styleName. This
makes it possible to match styles such as DejaVu Sans
Condensed and Ubuntu Medium.

The example fontsampler is updated so it can actually
sample all the different styles it lists.

Change-Id: I381effc74130311f98794cd07d30be10dee4fe45
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>