Adds a powerful plasma artillery shell that is able to incinerate nearly all fortifications, inspired by WH40k

stats:
new damage type: Plasma

Magma bomb damage:
1k physical
6.9k plasma

crafting costs:
recipe 1
4x advanced circuit
150x uranium-235
1x artillery shell

recipe 2 (space age only) :
4x advanced circuit
20x tungsten plate
200x lava

Graphics is repurposed in game sprites

to do:
figure out how to add lingering plasma fire
research orbital bombarbment mechanics