allow responses from non-subscribers if responses enabled

Value

Enable admins to run "hotlines" that receive "tips" from any random person without requiring that person to first subscribe to their signalboost channel.

Behavior

GIVEN an admin has already set RESPONSES ON on their channel

• WHEN a person who has not subscribed to that channel sends a non-command message to it
• THEN that message will be broadcast to all channel admins

Open Questions

• this is the fastest and easiest way to implement hotlines
• another version might make the "responses" toggle a 3-way switch: OFF/ON FOR SUBSCRIBERS/ON FOR ALL
• that seems overly complicated to me, but i don't have a better idea so i'd rather ship this and then ask what users want