Add OS X and iOS utility method file.
Add Security and CoreServices frameworks.
Update OS X entitlements.

* Remove root read/write exception.
* Enable security scoped bookmarks.
* Add read-write entitlement for the user downloads folder.
Add QStringToCFString helper method.
Add TrackInfoObject::getCanonicalLocation method.
Always codesign even if the files haven't changed.
Minor style.
Add notes about sandboxing to BasePlaylistFeature, CrateFeature, and SamplerBank.
Add mac.cpp to depends.py.
Add Sandbox, a singleton class for managing sandbox-related operations.
Load sandbox configuration at bootup and save it at shutdown.
Delete sandbox config in ~Sandbox().
Add sandbox support to the Library.

* Create a security token when adding or relocating a library directory.
* On startup, ask for access to user library directories if we don't have access.
Create a sandbox security token for files opened via the menu shortcut.
Create a sandbox security token when the user picks a new recordings directory.
Add simple wrappers around QFile and QDir that open/close a security bookmark.
Support creating sandbox tokens on iTunes and Traktor library selection.
Add copy constructors to MFile and MDir.
As a fallback (because by this point we should already have gotten access via
the means the file was loaded by the user), check and ask for sandbox access
right before requesting the track load to the engine.
Only add quick links that we have access to.