Implement ServerKey handling functions
Add function/methods dealing with ServerKeys to support auctioneer#17
The old Auc-Advanced had the following, which we could copy:
- GetServerKeyList() - returns a list of ServerKeys known to the module
- ChangeServerKey(oldKey, newKey) - moved/merged/whatever oldKey into newKey
These will become templates for future Stat modules, or any other module handling ServerKeys.
Propose implementing as methods (i.e. using ':')