Added failed and cancelled methods to TaskObserver; add adapter class for TaskObserver
Updated Javadocs to reflect changed semantics of TaskObserver's allFinished method
Updated javadocs for TaskObserver
Combined methods in TaskObserver into one allFinished(); created FinishStatus object to indicate how task iterators finished
Updated javadocs for task observers
Changed FinishStatus so that there's only one instance for success
Merge branch 'develop' of https://github.com/cytoscape/cytoscape-api into develop