Cleanup and extract more SQLite methods into the adapter

[andrewmarkle]

Based on Mike's feedback here we should continue extracted a few SQLite specific things:

One thing I do think still remains to be extracted into the adapters: the BaseConfig#database_path_for method, which only exists because the SQLite :database value might be a URI.

The idea I have in mind is to remove the "pathiness" from the database configs:

• delete the BaseConfig#database_path_for method
• remove the :database_path value from the TenantConfig hash
• move BaseConfig#coerce_path into the SQLite adapter
• and change SQLite#get_database_path into an instance variable @database_path that's computed in the initializer by calling coerce_path