remove slight delay when displaying callouts
fixes #189: improvements to annotation selection
 * allow selection of enabled annotations even without callout
 * added selection/deselection delegate methods
 * changed `enabled` -> `isEnabled` getter for MapKit consistency
 * simplification of some code
fix shape/circle hit detection passed on presence of fill color
fix problem with containers views & attribution iteration
fixes layer sorting regression introduced in f03045d
Merge branch 'develop' into arc