This combines the following changes:

* Event for group member added
* Event for group member removed
* Event for group created
* Event for grouping created
* Event for group updated
* Event for grouping updated
* Event for group deleted
* Event for grouping deleted
* Adding tests for deleting functions
* Bulk remove of members uses low-level API

    The reason for this is that a bulk event has no value from a logging
    perspective as it is not granular. So now, the API is a bit slower,
    but the information the events contain makes sense, beside this is
    not (and should not be) used very often.

    The reason why the events_trigger_legacy() is kept is because we
    cannot create a new event for this, as we don't encourage developers
    to created bulk events, for the reasons mentioned above.

    I removed the call that gets the user record from the function
    groups_remove_member() as it was not required and only appeared
    to check if the user existed. It appears to be safe not to do
    this check as nothing would fail down the line.

* Bulk unassign of groupings uses low-level API

    As the previous commit, we keep the legacy event for now as it would
    be wrong to create a new event to replace it.

    Also, the code has been changed to call the low-level API to unassign
    groups from groupins, even though at the moment there are no
    events for that function.

* Bulk deletion of groups uses low-level API

    Again, we keep the legacy event because replacing it would force
    us to create a new event that does not make sense. See MDL-41312.

* Bulk deleting of groupings uses low-level API
* Asserting legacy event name in unit tests
* Minor SQL query and code improvements