minor #6229 Rewrite EventDispatcher introduction (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Rewrite EventDispatcher introduction

| Q | A
| --- | ---
| Doc fix? | yes
| New docs? | no
| Applies to | 2.3+
| Fixed tickets | -

The event dispatcher docs were a bit old. I discovered it talked about bundles (while it's the components section).

While reviewing the article, I've also removed some redundant things (creating special sub event classes was mentioned many times). I've also tried to reword things a bit and introduce new (more commonly used) concepts for events.

Commits
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e148cb4 Rewrite EventDispatcher introduction

Author: xabbuh