Made the version checker optional

[viral32111]

Fixes #58.

• Added a global variable at the top of the main file.
• Added creating convar in the module open function.
• Added convar value checking in the doVersionCheck() function.

While I could have put all the code inside the module open function, I feel it's better to still let the timer be created so any convar changes prior to the server dehibernating (timers & think hooks starting) are applied.