Integrate new SoftDeletingTrait changes.

Signed-off-by: crynobone <crynobone@gmail.com>
Update doc.

Signed-off-by: crynobone <crynobone@gmail.com>
Add `Orchestra\Model\Eloquent` with `isSoftDeleting()` method. Closes
orchestral/control#22

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.2'