New reworked AnimatedSprite!

-New SpriteFrames editor, with support for drag&drop, multiple animation
sets, animation speed and loop.
-New AnimatedSprite, with support for all the new features!
AnimatedSprite3D has not been updated yet.
-Added support for drag&drop to other editors, such as resourcepreload,
sample library,  etc.

scene/scene_string_names.cpp

@@ -172,4 +172,6 @@ SceneStringNames::SceneStringNames() {
 	speed=StaticCString::create("speed");
 
 	path_pp=NodePath("..");
+
+	_default=StaticCString::create("default");
 }