Do not use saved position if it falls outside of primary screen

- Only use saved position if the coordinates fall inside of the primary screen
  Prevents problems for people with laptops that sometimes but not always use
  external screens.
- Since we now set window position in C++ instead of QML, drop the
  dependency on qml-module-qt-labs-settings module.

Closes #91

main.qml

@@ -8,7 +8,6 @@ import QtQuick.Window 2.2
 import QtQuick.Controls 2.2
 import QtQuick.Layouts 1.0
 import QtQuick.Controls.Material 2.2
-import Qt.labs.settings 1.0
 
 ApplicationWindow {
     id: window
@@ -768,13 +767,6 @@ ApplicationWindow {
         }
     }
 
-    /* Persistent settings */
-    Settings {
-        category: "General"
-        property alias x: window.x
-        property alias y: window.y
-    }
-
     /* Utility functions */
     function httpRequest(url, callback) {
         var xhr = new XMLHttpRequest();