Refactor ActivitiesHandlerMixin

[srosset81]

Problem

Right now, for every service using the ActivitiesHandlerMixin, a matching is made for all activities received or sent. The more services are doing this, the worst the performance become.

Solution

Create a ActivitiesWatcherService which is activated by default with the ActivityPub service.

This service as a watch action which takes a matcher (object or function), an actionName and a key.

On start, the ActivitiesHandlerMixin calls the watch function for all defined activities. The actionName is a processActivity action of this mixin.

The process action receives a key, a boxType (inbox/outbox), a dereferencedActivity and actorUri.

It thens calls the onEmit and onReceive methods of the corresponding activity.

[srosset81]

Ideas:

• Add a priority parameter
• Sort matchers by number of levels
• When comparing an activity between matchers, remember derefenced items https://github.com/assemblee-virtuelle/semapps/issues/1231
• Later: use JSON Schema and AVJ to match more complex activities without needing functions

[srosset81]

Done here #1240 but performances could be improved