As a user I want to be added to a new pool for channel if I already have set my wallet address

[peterpolman]

Problem
If a new asset pool is configured for a channel that already had a pool configured for it. The users wallet address is a member of the first pool, but will not automatically be a member for the second pool. This will cause calls to the API involving member access to fail (like giving a reward).

Solution
Increase validation for membership status in the discord bot and add MemberAdded, MemberRemoved contract events in the API to the event indexer so it can be cached.