Added automatic checking, darkmatch settings, etc

[darkshade9]

• Added cvar ban lists for darkmatch and force_xerp
• Made cvarbans_update.sh executable
• Added option check_interval which checks all cvar settings loaded via addcvarban every X seconds based on value provided
  • Omission of this option defaults it to 10 seconds
  • Setting it to '0' disables automatic checking while still loading cvar bans