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.
For example, if you do not have libboost-dev if one of the header files, say foo.h, has # include <someboostfile.h> then when an extension includes foo.h the extension build will fail.