debug module events panel

[yii-bot]

This issue has originally been reported by @Ragazzo at yiisoft/yii2#3842.
Moved here by @cebe.

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Usually when creating application and using EDA or SOA it is good to have ability to check events and data that they hold.
I think this panel would be useful in debug module, several modern fw also includes it.

The only thing here we have to solve is how to subscribe to all or part of events, since we dont have wildcard matching and we dont have any central point for event. My suggestion is to either add wildcard matching or introduce in events panel property neededEvents in format:

'neededEvents' => [
     'some\component\class' => [
          //list of events to subscribe
     ],
],

In the same way we can make exclude option. Data that will be collected upon each event is its public properties json encoded or we can use Yii2 var_export not sure about the last one though .

[klimov-paul]

Resolved by commit f69254a