Make Phaser.Text play nicely with scrolling, by using an explicit x, y

Phaser.Text currently uses an implicit x,y position, inferred from the PIXI position.

This breaks badly when you start scrolling Text objects (ie, in the game world) as the PIXI position is updated based on camera position, which is then used to adjust the PIXI position, which it then updated...

This pull request adds an explicit x,y position to Phaser.Text, which fixes scrolling, and should work with all existing uses of Phaser.Text except those that directly manipulate position.x and position.y.

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Also, there was a typo in RenderTexture. The identity matrix doesn't appear to be used anywhere, so it is perhaps superfluous anyway.