Define Event Lifecycle with Event objects for WebClient and RtmClient

[aoberoi]

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Description

The complete Event Lifecycle for the clients is not clearly documented anywhere. It should live on the Wiki pages for each of the clients.

Once the lifecycle is understood and documented, we can start defining types for Events. Each of these can have associated data. For example, the CLIENT_EVENTS.RTM.ATTEMPTING_RECONNECT event can emit an object of type ReconnectingEvent, which has properties attemptNumber, code (equal to the const for the type), etc.