Support extracting archives to the packages we build

* BuildHaikuPackage rule: Create the script that contains the extraction
  commands.
* build_haiku_package: Add extractFile() function (stripped down version
  from build_haiku_image).

In build_haiku_image the functionality was mainly used to extract the
optional packages, which is no longer done. We still need it e.g. for
the Wifi firmware packages that want to be extracted.
build_haiku_package: Print some progress info

Remove the output in extractFile(), though. The extracted packages are
so small that it doesn't matter anymore.
Fix reading attributes of directories

When reading an attribute of a directory there was no guarantee that the
underlying package would be open. When it wasn't reading an attribute
would fail, unless the attribute data were already cached. The reasons
for this are:
* UnpackingDirectory didn't forward the {Init,Uninit}VFS() calls to the
  underlying PackageDirectory.
* Only PackageFile was actually opening the package in InitVFS().

Now we forward the {Init,Uninit}VFS() calls in all cases -- even in
{Add,Remove}PackageNode(), when the active package node changes -- and
opening/closing the package is now done in
PackageNode::{Init,Uninit}VFS().