KAZOO-2764: callflow module to pickup any call from any user's group

I propose this is a subset of a use case of cf_intercept.  Perhaps if cf_intercept was refactored in addition to its current filtering ability it could handle this case as well?  If you disagree, I would prefer that this be renamed to cf_intercept_group for consistency since pickup and intercept are synonymous in the system.  Let me know what you think!  Otherwise the code looks good, thanks!