rename "subscriber responses" -> "hotline messages" (?)

STUB

The more times i say the words "subscriber responses" the more confusing i think it is. Particularly because the system sometimes (in fact always) sends a command response to subscriber responses. It would be nice to call those "responses to hotline messages" instead of "subscriber response responses."

If folks agree, I would propose the following renamings (which I could format into a proper card):

• RESPONSES ON / RESPONSES OFF -> HOTLINE ON / HOTLINE OFF
• [SUBSCRIBER RESPONSE:] -> [HOTLINE MESSAGE:]
• and corresponding changes in open issues that refer to "subscriber responses"

Implementation Note

• while doing this, also rename the channel.responsesEnabled db field to channel.hotlineOn (and change toggle function calls that hang off that logic)