MacOsX plist icon path fixed.
MacOsX 64bit support added.

This solves Segment fault 11 errors.
MacOsX content path fixed.
MacOsX dynamic horizons path.

In the max os x app container the path is lib/python2.7/horizon/engine.
So the path must be relative to the horizone module.
Mac Os X app container path fix.
Merge pull request #2177 from phaidon/mac-os-x

Several fixes to get our OS X app packaging into shape