Add more structure to allocation service registrations
During code-review, it has been noticed that there are a many registrations of allocation editors and support code with the allocation service within plugin activators. By that, it is hard to find to registrations, or spot faulty ones.
Cluster the allocation service registrations into private methods to group them.
(from redmine: issue id 3556, created on 2018-10-22, closed on 2018-10-25)