Remove broadcast Restriction on avatar.

[WifiLatency]

Depends on smogon/pokemon-showdown#10961

Client end of implementing the suggestion: https://www.smogon.com/forums/threads/avatar-avatar-to-be-broadcastable-showing-the-avatar-sprite-and-the-credit.3759095/

Removes the restriction on sending a broadcast prefix '!' with the avatar command to allow for users to broadcast it in chat. Prevents caching the selected avatar when using the '!' prefix to send the command.

[Zarel]

Hmm. This functionality is very different from /avatar. Maybe it should be a different command? How do other commands work?

Okay, I guess this sorta matches stuff like !roomintro? ...it's not a perfect match for any existing command, but oh well, close enough, I see no harm in this.

[Zarel]

Thanks!