New sounds for the BFG and plasma rifle

[uhbooh]

Made by MoonDeLaAxel and I, from CC0 sounds.

Sources
https://opengameart.org/content/space-laser
https://opengameart.org/content/doomsday-laser-cannon-sound-effect
https://opengameart.org/content/synthesized-explosion

[mc776]

I like them and they definitely work well as far as feel and timing are concerned, though they need to be much louder to sound right ingame.

Poking around on bart's OGA profile and they look legit so far... i'm not missing anything, am I?

[mc776]

If we're about to post a release, my opinion is that this PR should be deferred and the release should not be delayed because of this.

However, I'm not going to add the deferred tag because if the release is delayed for totally unrelated reasons and all outstanding issues are addressed on this PR, then it should be merged.

(frankly from what I had previously been led to believe there should have been a new FD release a couple hours before this PR had even been posted... what happened?) [i have been updated about this]

[mc776]

While testing #1296 I'd accidentally used a wad that had both that sound and these ones and yeah they are definitely not loud enough... like, the problem #1296 has just solved will have its equivalent pop up with technospiders and deathmatch opponents...

[uhbooh]

Yeah I'm aware that the sounds aren't very loud. My skills with audacity are not the best, but I'll try to fix them sometime soon.

[Snoucher]

I just noticed that in chocolate doom dsrxplod.wav doesn't play to it's end, which creates a noticeable cut off in the audio. We should probably do something about it before we merge it.