To make further changes easier (to better match with current Apple documentation...

To make further changes easier (to better match with current Apple documentation and code generated with Xcode), converted to automatic reference counting (ARC).  To simplify cleanup, made some plain C structs (the storage for sound and pending changes to a terminal) into Objective-C classes.  For similar reasons, and for better encapsulation, moved some file global variables into classes and promoted some instance variables in AngbandContext to full properties.  For ease of access to the application deleget, made some static functions into instance functions of the application delegate.