docs(events): Reword docs for hooks

Puts the location of the triggering of the hook before what it filters
Adds warnings for uncallable handlers in hooks/events.
Adds units for the warnings.
Injects logger into events/hooks services.
Ensures logger, events, and hooks are setup in right order in service provider.
Fixes small bug in DI container.
fix(groups): displays correct group content access options for each content access mode

Content access options for public groups:
 - Private
 - Logged in users
 - Public
 - Members of the group

Content access options for groups using members-only policy:
 - Private
 - Members of the group

Refs #6142
fix(groups): forces content accessibility to members_only for invisible groups

When user selects "Group members only" for group visibility, javascript sets
the group content accessibility field to "Members only" and disables it.

For existing groups the above is done also on server side.

When editing an existing public group, a warning is added under the group
content accessibility input saying that changing the setting won't change
the access permission of existing group content.