Add ability to use multi-word table names in migrations.

As a user, I frequently want to write table names like `users_read_articles` or `site_options`. These changes add support for that.

If the migration name is "create_users_read_articles_table", the table name will be `users_read_articles`. 

If the migration name is "create_users_read_articles", the table is `users_read_articles`

if the migration name is "create_table", the table name is `create`.

However, the third case does not make syntactical sense.