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/views/thumbnails.cpp

@@ -133,18 +133,21 @@ Thumbnails::~Thumbnails() {
 }
 
 bool Thumbnails::mouseButtonEvent(const nanogui::Vector2i &p, int button, bool down, int modifiers) {
-	if (button == 1) {
-		if (!down) {
-			context_menu_->setPosition(p - mPos);
-			context_menu_->setVisible(true);
-			return true;
+	bool r = View::mouseButtonEvent(p, button, down, modifiers);
+
+	if (!r) {
+		if (button == 1) {
+			if (!down) {
+				context_menu_->setPosition(p - mPos);
+				context_menu_->setVisible(true);
+				return true;
+			}
+		} else {
+			context_menu_->setVisible(false);
 		}
-	} else {
-		context_menu_->setVisible(false);
 	}
 
-	bool r = View::mouseButtonEvent(p, button, down, modifiers);
-	return r;
+	return true;
 }
 
 void Thumbnails::updateThumbnails() {