Add add and remove many to group

[SantiagoSotoC]

Snapcast allows n clients to be added and removed at a time, currently the library only allows adding and removing one client at a time. With minor changes to the current method this can be improved.
I can implement it, but first I want to know what interest there is to add this functionality and if you prefer that I add a new method or that the current method can receive a client or a list.