Make General preference pane scrollable

On some OSes/configurations/screens, the options on the General pane don't fit until the window is resized. Adding a scrollview helps in these cases.

resources/qml/Preferences/GeneralPage.qml

@@ -58,6 +58,11 @@ UM.PreferencesPage
         }
     }
 
+    ScrollView
+    {
+        width: parent.width
+        height: parent.height
+
         Column
         {
             //: Model used to check if a plugin exists
@@ -393,3 +398,4 @@ UM.PreferencesPage
             }
         }
     }
+}