Split code and reorganise headers
Created by: pieterdavid
The current solution of one header and one implementation has some advantages, but also makes it a bit harder to navigate the code. A possible splitting (thanks @sroychow!) is in https://github.com/sroychow/CMSJMECalculators/commit/92fbd315477cc29709f01f691b7d753269061f99 .
Unless there are strong reasons to change this now I'd prefer to wait a bit to gather feedback and see where this goes, such that it's easier to keep things in sync with the version in bamboo in the mean time.