Use redis-py 2.8.0.  (It supports RPOPLPUSH.)

Also recorded other requirements in requirements.txt.
Replaced auto-scroll toggle with pause/resume function.

Turning off auto-scroll when the terminal buffer is at maximum capacity
doesn't really works as advertised: the trimming done on the buffer has
the side effect of scrolling it.

Pause/resume fixes this problem by discarding messages that arrive
during the pause period and resuming message processing on resume.