Manage overlapping commands between clients

[raf924]

Right now, if two clients define the same command name and/or alias, both of them will have the possibility to execute it.
While this can be mitigated by disabling the command in one of the client's config, there should be a way to make it so only one client can use the command.

One solution would be to implement a first come first served algorithm.
Another would be to implement a load balancer.