Create separate class for making event modifications

WIP: should update unit tests before merging. Created pull request already for feedback.

Separate class simplifies the manager code a bit and should allow later better to make modifications else than main even, i.e. adding exceptions to recurring events. See commits for details.
assuming you have some kind of signalling in place, QTRY_COMPARE might be of interest. it'll wait only as long as necessary, not always 1000ms (and fail if it can't complete in a sane amount of time)