[ALOY-456] Support multiple databases in sql adapter

update

Alloy will support multiple sqlite databases in an app one of two ways: 1. By adding the *db_name* property to the *definition.adapter* object to identify the name of the database you would like to use/create. See here: [LINK COMING] 2. By loading from an existing database with the *db_file* field (from ALOY-345). Alloy will automatically use the basename of the file as the database. So if your db_file is "myapp.sqlite", then alloy will automatically use "myapp" as the database for all operations. It would be nice to be able to pass a database filename as part of the model.config.adapter when creating a SQL model - instead of defaulting to the _alloy_ database name. This would be helpful for situations where we might want to have multiple databases with differing configurations - for example: one database which is shared over iCloud, and one which is unshared and stored in the cahe directory.