[#1415] Notify adding and removing of handlers.

Problem description
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The chevah.utils logger is adding and removing handlers in the background without the server control.

We want to add some signaling code so that the server can at lease log an event when the logger is reconfigured.


Changes description
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Add 'add-handler' and 'remove-handler' notifications.

The added handlers have a dynamic name and should help with a more friendly log message.


How to try and test the changes
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reviewers @alibotean @bnickname 

Check that changes make sense.