Add underwater_structure/underwater_pictures for more entities

[jurgy]

Hi,

With the addition of tile_buildability_rules mods could create all sorts of mixed environment buildings. One of which is buildings on the water edge. For this it would be great if you added support for underwater_structure/underwater_pictures in the graphics for more entity types. Currently the former is only used for elevated rails supports and the latter for offshore pumps.

There are a bunch of offshore electric pole mods that could use it and I'm working on a dock which is an assembler underneath.

Thanks!