Inherit visibility

As of moai/moai-dev@cf311d50a0330a757bab396a0ce606b905f28a45, visibility can be inherited like color and transformation. I think it would be a good default for DisplayObjects to inherit visibility, too.

Maybe we should wait for a new Moai release before merging this, since the moai commit is not in the current release version (1.4p0).