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

All resource files should have matching line numbers, it helps managing
messages properly.

The attempt failed, but needs more investigation, so we keep it.

Conflicts:
	src/changes/changes.xml