Tweak layout for iOS 8
Tweak layout for iOS 8

iOS 8 introduces a new default callout size for when a subtitle is
present, adding more vertical margins.

mapbox/SMCalloutView,XBeg9/calloutview,Petvetbook/calloutview,Aiwis/calloutview,Suninus/calloutview,dmiedema/calloutview,Petvetbook/calloutview,mapbox/SMCalloutView,nfarina/calloutview,XBeg9/calloutview,nfarina/calloutview,Aiwis/calloutview,dmiedema/calloutview,Suninus/calloutview