Add TypingLabel extension module

[czyzby]

• Create a new KTX module that extends ktx-scene2d.
• Include and document another major dependency: com.rafaskoberg.gdx:typing-label.
• Add and test factory method for TypingLabel.
• Add utility extension methods that register event listeners.
  • Add support for multiple TypingListener instances.
• Consider adding custom DSL for TypingLabel tokens.

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TypingLabel is an interesting third-party extension that defines additional Scene2D actor: a label that appears to be typed in real time. It supports a wide range of special effects. It would be a nice addition to our Scene2D extensions.