only show aff pro migration if plugin is activate
use $step rather (stop debug notice)
fix aff pro migration issues. See commit desc

1. only select affiliates that have referrals or hits (do not port over
everyone)
2. Get correct earnings, referral count and hit visit count for aff
insert
3. default values for referral insert
ignore zero amount

Add setting to ignore zero amount referrals. If the amount is zero, then
do not store a referal
defaults for new affaliates