Adding AK5PFchs jet correction services

The last Jet-related item for 700 is a bug fix for AK5PFCHS payloads in the JEC services, which were not present before. This should have been added previously in the 6x series but I don't think it's necessary to backport because no one is using them so far. 

This also merges with PR 1804 already for your convenience.