Add a Movie Quit On Finish property to AnimationPlayer

This quits the project when an animation is done playing in the
given AnimationPlayer, but only in Movie Maker mode.
When this happens, a message is printed with the absolute path of the
AnimationPlayer node that caused the engine to quit.

This can be used to create videos that stop at a specified time
without having to write any script.

A report is now also printed to the console when the video is done
recording (as long as the engine was exited properly).
This report is unfortunately not always visible in the editor's
Output panel, as it's printed too late.

A method was also added to get the path to the output file from the
scripting API.

core/config/engine.cpp

@@ -246,6 +246,14 @@ void Engine::get_singletons(List<Singleton> *p_singletons) {
 	}
 }
 
+String Engine::get_write_movie_path() const {
+	return write_movie_path;
+}
+
+void Engine::set_write_movie_path(const String &p_path) {
+	write_movie_path = p_path;
+}
+
 void Engine::set_shader_cache_path(const String &p_path) {
 	shader_cache_path = p_path;
 }