Using deprecated FrameBuffer methods in jme3-examples

[stephengold]

PR #1401 deprecated the addColorTexture(Texture2D), setColorBuffer(Format), setColorTexture(Texture2D), setDepthBuffer(Format), and setDepthTexture(Texture2D) methods of FrameBuffer. However those methods are still used in jme3-examples.

As noted at #1401, it is difficult to understand how the replacement methods are meant to be used. Let's upgrade jme3-examples to use the new interface.

[riccardobl]

I've started converting the examples and added a quick documentation here: #1616 .

[stephengold]

Thanks @riccardobl