HaikuDepot: Rework to get actions working properly.

- BPackageManager doesn't (currently) support being reused for multiple
  differing actions, so instantiate it on the fly for each action to be
  performed.

- As such, pull the package action worker out of PackageManager and into
  MainWindow. Define abstract interface PackageActionHandler for other
  parts of Depot to use to instruct it to queue actions.

- Adjust other parts of code to take the above into account.
PackageListView: Force status field to update properly.