Force Text.QtRendering on button labels

Otherwise they look pixelated.

qml/NButton.qml

@@ -45,6 +45,7 @@ Rectangle {
         font.pixelSize: height*0.55
         color: font_color
         font.bold: true
+        renderType: Text.QtRendering
         // Workaround: Text.AutoText doesn't seem to work for properties (?)
         textFormat: text.indexOf(">") == -1 ? Text.PlainText : Text.RichText
         verticalAlignment: Text.AlignVCenter