Add Cocoa implementation of wxStandardPaths

Previously wxStandardPathsCF was used for all Mac builds and it used
FSFindFolder() (CoreFoundation) calls in Carbon builds, but many hard coded
values in Cocoa builds. The Cocoa implementation uses NSFileManager and
NSBundle to retrieve the folder locations from the system.

Closes https://github.com/wxWidgets/wxWidgets/pull/89

include/wx/stdpaths.h

@@ -187,6 +187,9 @@ protected:
     #if defined(__WINDOWS__)
         #include "wx/msw/stdpaths.h"
         #define wxHAS_NATIVE_STDPATHS
+    #elif defined(__WXOSX_COCOA__) || defined(__WXOSX_IPHONE__)
+        #include "wx/osx/cocoa/stdpaths.h"
+        #define wxHAS_NATIVE_STDPATHS
     // We want CoreFoundation paths on both CarbonLib and Darwin (for all ports)
     #elif defined(__WXMAC__) || defined(__DARWIN__)
         #include "wx/osx/core/stdpaths.h"