Handle ban command arguments as array

This provides a much more reliable way to handle arguments with spaces,
such as usernames.

The ban process's stdout and stderr are now redirected to the server,
in case they have output that would be good in the server's logs.

src/IConfig.ts

@@ -20,7 +20,7 @@ export default interface IConfig {
         node : string;
         displayname : string;
         motd : string;
-        bancmd : string;
+        bancmd : string | string[];
         moderatorEnabled : boolean;
         usernameblacklist : string[];
         maxChatLength : number;