Enable EventHandlers to receive WorkbookOpen event

[martinthenext]

The way it works now:

1. When user opens a spreadsheet this event gets handles by the automaton
2. Automaton gets go the state where it requests context from the server
3. After this it enters state Ready in which events are passed to handlers

We need to enable EventHandlers to also receive WorkbookOpen events. This could be done by passing the event to all handlers immediately after entering the Ready state.