* build_haiku_image: Remove MIME DB creation code.
* Rename beos_mime source directory to mime_db.
* Add rules to build the MIME DB in the source directory's jamfile.
* Add MIME DB directory to haiku.hpkg in data/mime_db.
* Add optional packages Zlib and Zlib-devel.
* Simplify the build feature section for zlib and also extract the
source package.
* Replace all remaining references to the zlib instance in the tree and
remove it.