[#75] Auditing fixes

From the issue:

• For users - only audit username and email
• For egroups - audit group identifier (instead of uuid)
• Channel snapshot - avoid calling target groups and users inside (its confusing)
• Computed users for intersection - it's confusing (in reality its duplicated from channel snapshot, so perhaps we can just add the key total to it
• Unsubscribed users is being audited twice

Closes #75