Added transition and music when completing a level

Added transition animation!!

Just an small update. I don't want to flood with small updates like this, but I wanted to test this feature from itch.io. The next updates will be more relevant and bigger.

Now, when you complete a level (Tutorial or Level 1, at the moment), small transition will play with a victory music. After this I want to show the "completed level" screen, but I'm working on it. Maybe in the next update :P