Update Mac platform documentation for Qt 5.

Update OS and compiler versions. Remove information
about universal builds (no longer longer supported).
Update information about Carbon and PowerPC (also
no longer supported). Update developer.apple.com
links. Update license information for Apple-contributed
code. Remove no longer referenced code snippets.
Fix misc other inaccuracies.

Change-Id: I1a861a9de55042ffe3ac5b425dd8fcf6648e822a
Reviewed-by: Casper van Donderen <casper.vandonderen@nokia.com>