Ports the supermatter engine from /vg/

The SM was originally developed for bay12, but I ported from the /vg/ fork.
Basically, it eats heat or atom/movables and generates radiation/power. Typical usage involves emitters and a cooling chamber.
Everything that touches it turns to dust. If it overheats, it explodes in a radius bigger than maxcap (there's a few loud radio warnings sent to common channel beforehand).
Currently, these are only obtainable through cargo for 100 points. Mapping changes to support building a supermatter engine from roundstart (such as adding one to secure storage and creating a designated room) would be appreciated, if someone feels up to the task please do so and PR it after this one is merged. The cargo crate comes locked and requires CE access.
I didn't port the large supermatter (a literally world-ending xenoarcheology artifact) or the stage six singularity (as that killed my test server with the lag), this is only the shard itself and its power/plasma generating properties.
Probably to avoid typecasting user as /mob/living in the first if(). I'll typecast it properly.