Fixed writing of ITRF frames before 2000 when generating CCSDS files.

Closes #878

See merge request orekit/orekit!228

Fixes #878

Conflicts:
	src/changes/changes.xml

Fixes #836

Fix #880 #881 AbsoluteDate toString with and without UTC offset

Closes #880 and #881

See merge request orekit/orekit!227

Previously there was no combination of methods that would generate a
rounded AbsoluteDate without UTC offset, which was the behavior of
AbsoluteDate.toString() in Orekit 10. Added methods and tests.

Previously the UTC offset was not copied from the original
TimeComponents to the rounded TimeComponents.

Fixes #849

The getters have been added for event shifter, slope filter and
predicate filter.

Fixes #837

Fixed initialization of maneuver trigger events.

Closes #874

See merge request orekit/orekit!226

Fixes #874