prepare-dev.py makes use of rb-site's internals for some setup, and

needs to do some initialization to get it working. To avoid

prepare-dev.py having to know much about the internals of this code,

this change introduces a new setup_rbsite() function that sets up the

logging and ConsoleUI.
This will shield prepare-dev.py from some upcoming changes to the

console initialization.

Tested both rb-site and prepare-dev.py in Python 2.7 and 3.9.