Added a dev package for debian (for trusty... to start)

There are three major commits in this PR (the first three):
      * The first one adds a dev version of skeleton that contains most of the DEBIAN directory as well as the primary file hierarchy for the actual package. 
      * The second commit adds the DEBIAN/control directory for trusty, which contains all the dependencies needed to build HHVM on trusty (so the headers will actually be useful)
      * The third commit updates the package script so it will actually create the package. On a high level, it installs the hhvm into a DESTDIR provided as the BUILD file. It then copies all the necessary files in BUILD into the appropriate place in the DPACKAGE folder and creates the package.
It seemed like a safe thing to do. I'm ok with not stopping hhvm if you think it is not a problem.