Add an actions package to abstract some simple behaviors

Summary

Add a rage.actions.* package to have objects that encapsulate behaviors to be executed, such as exiting a game, moving an object, etc.

Example

An Action would encapsulate a behavior. One behavior could be performing an "exit" action when the ESC key is pressed:

// ...
ExitGameAction exitAction = new ExitGameAction(this);
// ...
float time = getEngine().getElapsedTimeMillis();
exitAction.performAction(time);    // --> game.setState(Game.State.STOPPING); internally

or moving a rage.scene.Node forward when another key is pressed:

MoveForwardAction forwardAction = new MoveForwardAction(gameObjectNode);
// ...
float time = getEngine().getElapsedTimeMillis();
forwardAction.performAction(time); //

Benefits

It would help encapsulate behaviors in a cleaner way, make the code easier to understand, and so on. It could also be easier to integrate with other sub-systems that are willing to accept a rage.actions.Action type.