EventManager

[joe-bowman]

Summary

Presently we use a waitgroup-style int stored against the zone to order asynchronous operations; however:

1. this is difficult to reason about in the event of issues - it is unclear which operations have completed and decremented the counter, and which have not, without inspecting thousands of lines of log items.
2. it is not scalable: we can only control a single final event (e.g. redemption rate triggering) and cannot use it to arbitrarily order and schedule events
3. it is imperfect: it is possible that taking action X on reaching 0 might be unintentionally triggered before it is desired - and potentially triggered multiple times.

The successor to this will event manager:

• EventManager will be standalone module that other modules can hook into, declare callback handlers (in the same way that interchain queries does), and conditionally trigger events on the successful satisfaction of structured conditionals. The conditionals allow the expression of complex states; e.g. only trigger the redemption rate callback with arguments x,y and z, in the events that all unbondings, delegations and queries are completed.