HaikuDepot: Fix #10000.

- When switching selected packages, compare the new and old package action
  list. If they're the same, don't bother rebuilding the button bar.
HaikuDepot: Adjust displayed publisher.

- If available, show the package's copyright information for the
  publisher rather than the vendor, as the latter simply indicates
  the maintainer of the repository rather than the actual developers
  of the software contained in the package.