Set JDT on-save actions for task engine project.
Moved hierarchical task engine to its own interface & class.
Removed EmptyTaskEngine.
Add sequence task combinator.
Add @Override annotations.
Added lazy evaluation for sequence task.
Cleanup choice task evaluator.
Fix incorrect call to choiceSucceeds in ChoiceTaskEvaluator.
Cleanup.
Cleanup.
Merge branch 'master' into prop-lists

Conflicts:
	org.spoofax.meta.runtime.libraries/task/tasks.str