* Update fixtures to match the current storage schema.
The existing files were a little misleading. This commit moves them into an 'old'
directory, and creates a new 'v1empty.db'.
* Add empty example Toodle database.
* Rename :item/labels to :item/label in Toodle schema.
* Define 'cargo cli' as an alias to run the Mentat CLI.
* v1empty.db: an empty v1 DB, which is the original on-disk format.
* v2empty.db: an empty v2 DB. This includes bootstrapped schema metadata attributes.
* v1tofino.db: a v1 DB that was created by Tofino.
