Tweak the annotations so they respect MKAnnotationView's calloutOffset (and make sure we use it!)

Signed-off-by: Blake Skinner <bskinner@mit.edu>
Clean up the delegate methods. We only care about the will/didRefresh notifications so keep it simple for now.

Signed-off-by: Blake Skinner <bskinner@mit.edu>
Fix a bug where a callout may not be dismissed if it's targeted annotation is deleted

Signed-off-by: Blake Skinner <bskinner@mit.edu>