v0.4 - Undo/Redo, mirrored drawing, lighten/darken tool and more!

In this commit:
- Added notification labels that appear when the user does an action (for undoing, redoing and saving)
- Fixed symmetry with custom brushes.
- In Main.gd, current_save_path and current_export_path get cleared when the user creates a new drawing or opens one.

v0.4 of Pixelorama is out! Check https://functionoverload590613498.wordpress.com/2019/11/13/pixelorama-v0-4-is-out/ for the full changelog.

Scripts/NotificationLabel.gd

@@ -0,0 +1,15 @@
+extends Label
+
+# Declare member variables here. Examples:
+# var a = 2
+# var b = "text"
+
+# Called when the node enters the scene tree for the first time.
+func _ready() -> void:
+	var tween := $Tween
+	tween.interpolate_property(self, "rect_position", rect_position, Vector2(rect_position.x, rect_position.y - 100), 1, Tween.TRANS_LINEAR, Tween.EASE_OUT)
+	tween.interpolate_property(self, "modulate", modulate, Color(modulate.r, modulate.g, modulate.b, 0), 1, Tween.TRANS_LINEAR, Tween.EASE_OUT)
+	tween.start()
+
+func _on_Timer_timeout() -> void:
+	queue_free()