HaikuDepot: WIP to open .hpkg files.

 * When opening .hpkg files, shows just the PackageInfoView in a smaller
   window.
 * PackageInfo constructor with BPackageInfo argument
 * Default pkg icon has a single instance only. Before, there would be another
   instance for each repository refresh.

TODO:
 * Install button on single package view is non functional
 * Probably needs to do someting different when opening .hpkg from an
   installed packages folder (show the regular list and focus that package?).
 * The filter view and list view are still constructed for the single package
   mode.
 * ...
HaikuDepot: Revert change regarding publisher name

It is now again the first string from the copyrights list, unless there is
no copyrights list, in which case the vendor string is used.