Update to ARC
Remove workaround for signatureWithObjCTypes:

This method was made available in 10.5 along with documentation.
Remove commented out code
Use Foundation (Core) data types
Reorganized Dialog.mm

Mainly ensure that the class implementation follows it's interface declaration.
Remove unneeded import of Carbon.h
Do not use deprecated methods for reading/writing pists

These were deprecated because they do not follow proper Cocoa memory management rules.