Switch windows to SDL2. Fixes #4945.
Switch linux to packaged SDL2 2.0.2. Fixes #5228.
Remove legacy renderers.
Drags death sounds out of RenderInfantry into a separate DeathSounds trait.

Play death sounds with a new PlayVoiceLocal so they don't use full volume regardless of position relative to camera.
Adds option for alternative burn and zap death sounds.
Renames RenderInfantry's UseInfantryDeath trait to SpawnsCorpse.

Removes hack from ra desert shellmap.
Removes rank signs from ships on desert shellmap.

Closes #4963.
Merge pull request #5236 from reaperrr/deathsound

Closes #2392
Closes #4680
Merge pull request #5235 from pchote/sdl2

Remove SDL 1.2 and Cg support
Remove an outdated hack from Renderer.
Reference mono's libfreetype under osx.
Make TeslaZap color palette customizable.
Make MuzzleFlash palette customizable.
Move winforms crash dialog into an external helper.
Add a native crash dialog for OSX.
Remove Windows.Forms dependencies from game and utility. Fixes #4348.
Merge pull request #5238 from reaperrr/more-palettes02

More palette un-hardcoding
Merge pull request #5244 from pchote/bye-bye-winforms

Remove X11 dependency from OSX.
Closes #3872
Closes #4348