Resolves #343 GUI and Frame Refactor

Major rewrite of the GUI into a module and view form, also using a new Feed class. The frame and frameset data structures have also been rewritten to support memory pooling and response frames.

applications/gui2/src/modules/addsource.cpp

@@ -13,14 +13,21 @@ void AddCtrl::init() {
 }
 
 void AddCtrl::show() {
-	if (screen->childIndex(window) == -1) {
+	// Note: By chance, the pointer can in fact pass this test as another
+	// widget gets allocated to the exact same address
+	if (!window || screen->childIndex(window) == -1) {
 		window = new ftl::gui2::AddSourceWindow(screen, this);
 	}
-	window->requestFocus();
 	window->setVisible(true);
+	window->requestFocus();
 	screen->performLayout();
 }
 
+void AddCtrl::disposeWindow() {
+	window->dispose();
+	window = nullptr;
+}
+
 ftl::Configurable *AddCtrl::add(const std::string &uri) {
 	try {
 		if (io->feed()->sourceActive(uri)) {