Add the obvious node_ref constructor
packagefs Package: Add getters for device and node ID
packagefs: Move the package loading code to Package

* Volume::_LoadPackage() -> Package::Load()
* Volume::_DomainEntryCreated(): Pull a bit of code into a new
  _LoadPackage() method for reuse.
packagefs: ioctls for getting and changing package activation

* Add PACKAGE_FS_OPERATION_GET_PACKAGE_INFOS which returns the node refs
  of all packages activated.
* Add PACKAGE_FS_OPERATION_CHANGE_ACTIVATION to activate/deactivate
  multiple packages.
package daemon: Add package monitoring and de-/activation

* packagefs: Disable (comment out) node monitoring of the packages
  directory.
* package daemon:
  - When a packagefs volume is added load the respective packages
    directory and get from the volume which of the packages are
    activated.
  - Add node monitoring for the packages directory and
    activate/deactivate packages as packages are added/removed.