Changed IEDs into firebombs.

Changed IEDs into firebombs to curtail the amount of station damage done whilst keeping IEDs useful and still keeping fuel tank bombs a useful saboteur's tool.

Their fuse time is a bit more variable too, including a 1 in 10 chance of them going off practically straight away (note: this is counter-able by the user wearing a fire-suit, git gud and l2p)
Funfact: pickweight doesn't like numbers unless they're in a string.
spaces
Merge branch 'master' of https://github.com/tgstation/-tg-station into iracocktail
Merge branch 'master' of https://github.com/tgstation/-tg-station into iracocktail
Changed the IEDs name and desc to firebombs
Changed changelog entry per request
Changed the weighting on blast range, 4 turns out to be quite big so shouldn't happen too often
Merge pull request #3856 from Malkevin/iracocktail

Changed IEDs into firebombs.