2022 total rewrite for optimization. Functionality should remain mostly the same, but with a much lower performance impact.

Added a new convar due to popular demand:
"extwater_oilbarrels": Explosive barrel props will not be extinguished if set to false, restoring their functionality in the HL2 campaign.

- Doused objects will make a "fwoosh" sound.
- Two new convars:
-- "extwater_enabled": Enable the addon's effect.
-- "extwater_sound": Turn the aforementioned sound effect on or off.
- Revised code based on code_gs' suggestions.
- Removed the debug print statement.