Added AnimationTag class

Replaces nested Global.animation_tags arrays. Also replaced array.duplicate(true) with looping through the array and creating a new class for each array element, because duplicate(true) does not create new classes, unfortunately, which was causing issues with undo/redo.

src/Classes/AnimationTag.gd

@@ -0,0 +1,15 @@
+class_name AnimationTag extends Reference
+# A class for frame tag properties
+
+
+var name : String
+var color : Color
+var from : int
+var to : int
+
+
+func _init(_name, _color, _from, _to) -> void:
+	name = _name
+	color = _color
+	from = _from
+	to = _to