Refactor|libcore: Renamed PackageFolder => ArchiveFolder

A more apt name for this class, as it is basically just a folder with
an ArchiveFeed. Packages might reside in other kinds of files as well,
so it does not make sense to tie that functionality solely to
PackageFolder.
Cleanup
libcore: Minor improvements

String has a constructor for wide char arrays, and Version can parse
numbers with less than three components.
libcore|FS: Added Package, PackageLoader, PackageFeed

PackageLoader is responsible for knowing which packages are available
and loaded. PackageFeed links the loaded packages under a folder.
Package represents a loaded package.