Support iOS application bundle structure.

Ninja was defaulting to building the mac desktop bundle structure. Added a way
to build the iOS structure. This is triggered by a target having an
IPHONEOS_DEPLOYMENT_TARGET entry in their xcode_settings.

BUG=chromium:236517
Review URL: https://codereview.chromium.org/14367052/

patch from Justin Cohen <justincohen@chromium.org>!



git-svn-id: http://gyp.googlecode.com/svn/trunk@1630 78cadc50-ecff-11dd-a971-7dbc132099af