simple refactoring for the reports: maybe this gets it below D
major refactoring of reports into separare classes

reports now live in separate classes: This brought up several issues
with buggy templates; lots of duplicate code has now been removed.

Still needs some view-testing, and maybe some unit-testing for the
service.
Worked in the review-remarks, added proper coypright notices where missing
abstract-class is ActiveRecord only, removing it.
added changelog-entry
Merge pull request #484 from opf/refactor/reports_controller

simple refactoring for the reports: maybe this gets it below D