Sqlite database does not respect database_id

Databases should be exported as `databases/SQLite-my_id.sql` , given `database SQLite, :my_id do |db|`
It incorrectly exported as `databases/something.sql` , where `something` was the filename.  This leads to backups of databases being overwritten if they have the same name.
This commit also simplifies the model, by relating one model to one file.