Feature request: add option to automatically scroll chat to start of unread messages

When I switch chat to a conversation or channel that has a bunch of unread messages, the first thing I have to do is carefully scroll upward searching for the little orange line that marks the beginning of the sequence of unread messages. Every single time. Life would be improved if the UI could just automatically do this when the channel is changed -- the screen's going to be replacing the list of messages displayed anyway, so why not put things in the most useful reading state to be in after the context switch? (And of course to be friendly it probably should be governed by an options setting to accommodate the inevitable people whose cognitive style rejects such automation.)

The issue concerns the chat UI when switching conversations or channels, including the orange unread-message marker and an optional setting. Start by locating the context-switch behavior and the code that positions the message list around unread messages. Done means the view can move to the start of unread messages on channel change and users can disable that automation.

Written by the indexing model from the issue text.