[4.2] Add password helper to the schema Blueprint

Like the existing `rememberToken()` helper, this makes it easy to create a 60 character string column for a hashed password (I actually forget on every new project that the hash is 60 characters and have to go look it up in an earlier project to check).

It will default to a column named password, but allows you to pick your own name for the column if you prefer.
Don't really see the benefit.

> PASSWORD_DEFAULT - Use the bcrypt algorithm (default as of PHP 5.5.0). Note that this constant is designed to change over time as new and stronger algorithms are added to PHP. For that reason, the length of the result from using this identifier can change over time. Therefore, it is recommended to store the result in a database column that can expand beyond 60 characters (255 characters would be a good choice). 
> <http://php.net/manual/en/function.password-hash.php>