Update tmxrasterizer OSX install

On OSX, "tmxrasterizer" is currently built as an app bundle by default and is also not included in the file dmg distribution file.

I use it as a command line tool in my xcode build process and I'm also planning on creating a tmx optimiser utility which I will base off tmxrasterizer so just wanted to get things setup to use in an easier way on OSX.

I've modified the tmxrasterizer.pro file to build it as a command line file only and then modified the ruby script to copy it into the Tiled.app/Content/MacOS directory.  From there the framework paths are fixed and can be run using the libs bundled in the tiled.app.

I've built and tested this on a mac mini using OSX 10.9.4.