Feature Request: Ability to change username

Changing the own username is kinda the basic functionality one (or at least I) would expect to be possible. However it appears that this is only possible by disconnecting from the server and then reconnecting to it with a different name.

Once #3778 gets fixed, the double-click action for the own user should be free again which could be mapped to changing ones username.

If I understand the code correctly this would require to send a UserState message to the server that contains the desired username. https://github.com/mumble-voip/mumble/blob/987953c008f2d6ba205bc3734607106dafae5258/src/Mumble.proto#L167-L170

If this isn't possible (because e.g. the name is invalid or already in use) I assume the server would answer with a PermissionDeniedmessage with UserName as the "DenyType". https://github.com/mumble-voip/mumble/blob/987953c008f2d6ba205bc3734607106dafae5258/src/Mumble.proto#L279-L280