Add width, height in addition to minimumWidth, minumumHeight to fix retina issue on OSX

Without these additions, windows (preferences, wizards, about) open larger than fullscreen, making some controls inaccessible

Fixes CURA-504

plugins/ChangeLogPlugin/ChangeLog.qml

@@ -11,8 +11,10 @@ import UM 1.1 as UM
 UM.Dialog
 {
     id: base
-    minimumWidth: 400
-    minimumHeight: 300
+    minimumWidth: 400 * Screen.devicePixelRatio
+    minimumHeight: 300 * Screen.devicePixelRatio
+    width: minimumWidth
+    height: minimumHeight
     title: catalog.i18nc("@label", "Changelog")
 
     ScrollView

resources/qml/AboutDialog.qml

@@ -13,8 +13,11 @@ UM.Dialog
 
     //: About dialog title
     title: catalog.i18nc("@title:window","About Cura")
-    minimumWidth: 400
-    minimumHeight: 300;
+
+    minimumWidth: 400 * Screen.devicePixelRatio
+    minimumHeight: 300 * Screen.devicePixelRatio
+    width: minimumWidth
+    height: minimumHeight
     //UM.I18nCatalog { id: catalog; }