Standardise provider interfaces in Sakai

In Sakai there are several interfaces that can be implemented and set at runtime to customise the behaviour of Sakai. Example of these are:

org.sakaiproject.user.api.CandidateDetailProvider
org.sakaiproject.user.api.UserDirectoryProvider
org.sakaiproject.authz.api.GroupProvider
org.sakaiproject.contentreview.service.ContentReviewService
org.sakaiproject.coursemanagement.api.CourseManagementService

However these have different behaviour and ways of being configured. We should look if there is a common best practice that we should adopt across the board.