open-to-sealed.8 : move remaining non-fundamental methods to extensio… …ns in suitable modules

open-to-sealed.7 : move mapOverlay extension to geo package 

open-to-sealed.6 : convert individual mapOverlay properties to extens… …ions

open-to-sealed.5 : get compiling again - remove the now incorrect override modifiers - implement ItineraryItem.mapOverlay as an exhaustive with expr that calls the mapOverlay method of subclasses. Highlighted as smart-casts.

open-to-sealed.4 : extract mapOverlay as an extension (does not compile) 

open-to-sealed.3 : add ItineraryItem.toCalendarEvent() 

open-to-sealed.2 : make ItineraryItem a sealed class 

open-to-sealed.1 : move classes to same source file 

open-to-sealed.0 : baseline for new open to sealed classes refactoring 

exceptions-to-values.9 : process IOException