Create fireworks when new WR is set/on match end

[mxpph]

When a pure world record is set fireworks will go off above the button. Necessary sprites and audio are in the resources folder (as requested by naz).

[fireblizzard]

Off the top of my head there are a couple things to be tested here:

• [x] That everything works fine when more than 1 player finish around the same time, so that 2 firework sprites or more are visible at a time.
• [x] That the sprite entity is removed after it finished, as we don't want to surpass the visible entity limit (256?) because otherwise normal entities of the map will start becoming invisible.

I will try to test these later today in SourceRuns's Experimental server. If it works fine I'll push it to the rest of SourceRuns servers for more playtesting and hopefully in less than a week it should be merged into master.

[fireblizzard]

Merged into the unstable branch, refactoring it a bit. I almost don't have experience with PRs and maybe I had to request that you do the refactoring and PR to unstable instead of master but whatever, this feature is now in unstable.

[mxpph]

Well I guess this PR is redundant now. I'll close it. Thanks!