Some fixes for 3.1.0rc1

I fixed a few things when I upgraded to 3.1.0rc1:

Removed what it seemed to be a debugging print.
Fixed legend in `celery events` for moving around with j/k keys.
The cursors display was not thread safe which could cause the screen to get corrupted at times.
Formatting of float value for runtime was invalid in celery events.
Umbrella commands were not working for celery multi.
Nasty fix to make django's `manage.py celery worker --detach` command work.