Add support for building macOS disk image installers (drag and drop)

This will require support for writing binary data so QBS can handle the (quite difficult) task of writing the appropriate .DS_Store file to the dmg instead of requiring users to provide one themselves (though this should still be an option). The former option is most preferable because storing a pre-made .DS_Store binary blob is difficult to tweak and attempting to run AppleScript at runtime to generate one is potentially unstable and is awkward to make reusable. That approach also results in backwards compatibility issues since .DS_Store files generated on newer systems may not work on older ones.

There are a number of third party resources (including a Perl module) we can reference for knowledge of the file format and build process:

• https://wiki.mozilla.org/DS_Store_File_Format
• http://search.cpan.org/~wiml/Mac-Finder-DSStore/
• http://clanmills.com/articles/macinstallers/DSStoreFormat.html http://web.archive.org/web/20130414103528/http://clanmills.com/articles/macinstallers/DSStoreFormat.html
• http://clanmills.com/articles/macinstallers/ http://web.archive.org/web/20130903194002/http://clanmills.com/articles/macinstallers/ (this one's quite useful)
• https://mxr.mozilla.org/mozilla-central/source/build/package/mac_osx/pkg-dmg?raw=1

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For some reason, `hdiutil makehybrid` causes my DVD drive to emit a strange noise. Disabling related kexts silences it I'd love a better solution if anyone else happens to know.

sudo kextunload /System/Library/Extensions/IOSCSIArchitectureModelFamily.kext/Contents/PlugIns/IOSCSIMultimediaCommandsDevice.kext 
sudo kextunload /System/Library/Extensions/IOBDStorageFamily.kext 
sudo kextunload /System/Library/Extensions/IODVDStorageFamily.kext 
sudo kextunload /System/Library/Extensions/IOCDStorageFamily.kext