Update All ConVar Declarations

Currently, the vast majority of the convars lying around look like this:

if not ConVarExists("mining_asteroidRespawnEnable") then
	CreateConVar("mining_asteroidRespawnEnable", 1, {FCVAR_NOTIFY, FCVAR_ARCHIVE})
end

They're serviceable, but they don't have Help text, and they're not stored in variables, needing to be referenced with GetConVar("Name") which is somewhat slower. Finally, the entire method of checking if the convar exists before making it is completely useless, running CreateConVar without checking is perfectly safe in my tests.

Please update all ConVar creations to this format, and update references in the code to match:

local cvar_asteroidRespawn = CreateConVar("mining_asteroidRespawnEnable", 1, {FCVAR_NOTIFY, FCVAR_ARCHIVE}, "Toggle respawning of asteroids for limited or unlimited resources.")