package daemon: Initial old packages state support

* VolumeState: Move locking to Volume.
* Package: Pull the file related functionality into new class
PackageFile. A Package refers to a PackageFile. A PackageFile can be
referenced by multiple Packages. PackageFiles are managed by the new
PackageFileManager.
* CommitTransactionHandler: Clone the passed volume state.
* Volume now manages two VolumeStates: A state reflecting the currently
active packages and the latest state (i.e. the one reflecting the
situation of the packages directory). Usually the two are the same,
unless an old state has been booted.
* The client interface hasn't been adjusted yet. Clients only see the
latest state.

package daemon: Initial old packages state support

* VolumeState: Move locking to Volume.
* Package: Pull the file related functionality into new class
PackageFile. A Package refers to a PackageFile. A PackageFile can be
referenced by multiple Packages. PackageFiles are managed by the new
PackageFileManager.
* CommitTransactionHandler: Clone the passed volume state.
* Volume now manages two VolumeStates: A state reflecting the currently
active packages and the latest state (i.e. the one reflecting the
situation of the packages directory). Usually the two are the same,
unless an old state has been booted.
* The client interface hasn't been adjusted yet. Clients only see the
latest state.