Added a listener for vector features

There are new two vector loading listeners: one that returns the notification with the feature data and another that simply provides the notification.
Altered to prevent unnecessary callbacks

If we don't have the appropriate listener, then we don't need the callback to be invoked.
Added a listener behavior for view changes.

This listener will be invoked whenever the map view is changed (zoomed or panned).
Added files missing from last commit.
Added a listener that provides feature in extent data.

Similar to the listener that provides the current view extent except it also provides all of the feature data in the extent.