[Tizen] Installer crashes when path is directory

An uninitialized variable was used in case of installation from directory.
This patch adds a UnpackedWGTPackage class.

BUG=XWALK-2674
hm, this is actually a change in UX: installing from a directory is a new feature. IMO it looks a bit weird, but anyway there should have been an "intent to implement" mail before this patch.

@baleboy is it planned functionality?