Refactor the PrintSetupSelector

The file was splitted in several other files to improve readability.
There is a new folder called PrintSetupSelector where all those files
will be.

Contributes to CURA-5941.

resources/qml/PrintSetupSelector/CustomPrintSetup.qml

@@ -0,0 +1,10 @@
+// Copyright (c) 2018 Ultimaker B.V.
+// Cura is released under the terms of the LGPLv3 or higher.
+
+import QtQuick 2.7
+import QtQuick.Controls 2.0
+
+import "../Settings"
+
+SettingView {
+}