Added SteamCMD update checker

Created update checker using SteamCMD. After some advice from SteamDB on
Twitter I found out you can get depot files directly from SteamCMD.
SteamDB update checker is still present however is only used if steamcmd
fails (SteamDB advised they cannot guarantee the accuracy of there depot
files).

https://twitter.com/SteamDB/status/546720685260017664

There are 3 different update checkers available as a failover and will
run in the following order as required.

1. SteamCMD update checker
2. SteamDB.info update checker
3. Server Log update checker