Open DB from CLI

[fluffyemily]

• Allow db name to be provided as an argument to the CLI tool on startup. This should connect to the provided db.
• If no db name is provided, a temporary database should be started.
• If no db exists with the provided name, a new db of that name should be created.
• Implement an .open command to open a database by name from inside the shell.
• If the temporary db is running when a new database is chosen, discard the temp db.