alignment worker recalculation triggers for other kinds of modifications on the alignment view

The demo featureCounter groovy script developed for JAL-2068 provides a way to create annotation derived from feature distributions on the alignment. However, alignment annotation workers are currently only updated when sequence data are modified - so even if the feature settings are modified to show new examples of the features being calculated, the alignment needs to be edited to force recalculation.

Ideally, workers dependent on other data should be able to register themselves for different kinds of update (alignment edits, non-edits [ e.g. reorderings], feature creation/import, feature display state changes, annotation import/creation, annotation display changes, etc).