Item_Model::save(). This makes creating albums similar to editing
them and makes it difficult to create an album poorly. I expect to be
able to remove a lot of code from the photo and movie helper because
it's duplicated here.
In order to do this, I refactored ORM_MPTT::add_to_parent() into
ORM_MPTT::save() so we now add it to the parent when we do save. This
allows us to call save() only once which saves a database call per
add.
The Albums_Controller logic is roughly the same as before.
Haven't updated the tests yet, they're going to fail miserably since
many of them depend on album::create() which is now gone.