Texture update (re) corrections.

Further improved the way that textures are updated as they were being updated for the wrong frame. Spriter does this very weirdly.
Removed the old fake frame with a zero duration on initialisation.

Improved startAnimation so that any artefacts from a prior animation are removed. This works but it does result in a blink. We really need to add an intelligent morph between animations that caters for sprites moving around in the spriter node hierarchy.

Setting a texture directly was causing a problem with SpriteKit so textures are changed via a SKAction now (seems unnecessary but it works).