Have the zoom slider panel dispatch events to reference frame using Guava EventBus
Repaint IGV using events from Guava eventbus

rename ZoomChange to ViewChange
Use DragStoppedEvents instead of explicit method calls
Change to event bus for handling chromosome change events and zoom changes.

Generally I think this looks better from a code-cleanliness standpoint; we don't need explicit repaint calls everywhere.
Remove explicit observable of reference frame chromosome used by region of interest, use event bus instead.

Have IGV receive chromosome change events, instead of calling IGV explicitly
Improve handling of history recording, keep it all in the events and use session to listen
Merge pull request #30 from broadinstitute/ViewEvents

ReferenceFrame Events