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

@@ -133,8 +133,6 @@ Thumbnails::~Thumbnails() {
 }
 
 bool Thumbnails::mouseButtonEvent(const nanogui::Vector2i &p, int button, bool down, int modifiers) {
-	bool r = View::mouseButtonEvent(p, button, down, modifiers);
-
 	if (button == 1) {
 		if (!down) {
 			context_menu_->setPosition(p - mPos);
@@ -144,6 +142,8 @@ bool Thumbnails::mouseButtonEvent(const nanogui::Vector2i &p, int button, bool d
 	} else {
 		context_menu_->setVisible(false);
 	}
+
+	bool r = View::mouseButtonEvent(p, button, down, modifiers);
 	return r;
 }