BugFix for PingPong animation and added additional methods to SKSprite

BugFix: 

After the first animation cycle through the frames when ping ping is
activated, the 1st and last frames were both being displayed 2x longer
than they should be.

Methods Added:

setColor() - Sets the color tint of the sharedMesh quad at runtime

rotate() - Rotates the sprite about the z-axis

playAnimation() - Starts an animation only if one is not currently
playing, or the one requested is not the one currently playing.