Make WP Tiles optionally BEM-notation compatible

[Volker-E]

It'd be great if WP Tiles would support an optional custom Block Class and/or BEM notation support. It has proven to give advantage in orientating in large code bases more easily.

So wp-tiles-tile class could become tiles__tile and wp-tiles-image-animated wp-tiles-image-scale-up could become tiles__image--animated tiles__image--scale-up.