QtQuick.Dialogs DefaultFontDialog: visual improvements

QtQuick.Dialogs DefaultFontDialog: visual improvements

Layout is taller and less wide, by putting weight, style and sample
below the other list views.  It's more resolution-independent and
looks reasonable by default on Android.  Renamed Others to Style.
Made column headings bold.  Text in selected ListItem delegates
are in a contrasting color.  Delegates are taller so they are
easier to select by touch.

Task-number: QTBUG-34157
Change-Id: Ia0c96c8556835d689d3c2fd5e2c0d34e421aff76
Reviewed-by: Liang Qi <liang.qi@digia.com>