Use more semantically appropriate fonts icon in properties dialog

`preferences-desktop-font` is only supposed to be used for settings
pages where large colorful icons are being shown. As such, it looks
out of place among the other monochrome icons in this dialog.

This MR replaces it with the more semantically correct monochrome
`dialog-text-and-font` icon.

ui/propertiesdialog.cpp

@@ -126,7 +126,7 @@ PropertiesDialog::PropertiesDialog(QWidget *parent, Okular::Document *doc)
         // create fonts tab and layout it
         QFrame *page2 = new QFrame();
         m_fontPage = addPage(page2, i18n("&Fonts"));
-        m_fontPage->setIcon( QIcon::fromTheme( QStringLiteral("preferences-desktop-font") ) );
+        m_fontPage->setIcon( QIcon::fromTheme( QStringLiteral("dialog-text-and-font") ) );
         QVBoxLayout *page2Layout = new QVBoxLayout(page2);
         // add a tree view
         QTreeView *view = new QTreeView(page2);