add event log

Value

• persist metrics about channels and users that will persist after channels are destroyed or users leave all channels

Behavior

• every time a channel is created or destroyed, append a channel_created or channel_destroyed event (with timestamp and hashed channel phone number) to the event log
• every time a unique user is created or destroyed, append a user_created or user_destroyed event (with timestamp and hashed member phone number) to the log

Implemenation notes

• use either strHash or sha256 for the hashing algo
• to detect new user: after creating membership, count memberships with user phone number, if only 1 exists, add creation event
• to detect user destruction: after deleting membership, count memberships with user phone number, if none exist, add destruction event