Fix viewing apps and CLI streaming with Qt 5.11 and earlier

Arrow function expressions are not supported in QML until Qt 5.12.

Fixes #1350
Closes #1391

app/gui/AppView.qml

@@ -350,7 +350,7 @@ CenteredGridView {
 
         function quitApp() {
             var component = Qt.createComponent("QuitSegue.qml")
-            var params = {"appName": appName, "quitRunningAppFn": () => appModel.quitRunningApp()}
+            var params = {"appName": appName, "quitRunningAppFn": function() { appModel.quitRunningApp() }}
             if (segueToStream) {
                 // Store the session and app name if we're going to stream after
                 // successfully quitting the old app.