Document application events

We should (I mean, I should) take a look at application's event.

https://github.com/nette/application/blob/3cde3b73e54cd928e6c6249b5efa655abcdf3233/src/Application/Application.php#L31-L47

- onStartup
- onShutdown
- onRequest
- onPresenter
- onResponse
- onError

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Ref: https://forum.nette.org/cs/34553-logovani-kazdeho-requestu-a-kazde-response-do-elastiku#p216507
