Additional layers to actor rendering

[ErinaSugino]

Add additional layers to the actor rendering for individually animatable ears and tails.
Provide default blank image to reduce log spam, add option to species file to define usages of these sprites. (potentially add option for general custom override of files?)
Layering? This dips into Relayer territory.

Fixes Neki ear misplacement on dildo position and offers more freedom and control in general.

[ErinaSugino]

Forgot to link d7b6d60