Adding `$table->rememberToken()` method to schema builder

Includes tests

Signed-off-by: Adam Engebretson <adam@enge.me>
Adding `$table->rememberToken()` DocBlocks

Signed-off-by: Adam Engebretson <adam@enge.me>
Merge pull request #4622 from adamgoose/4.2

Adding `$table->rememberToken()` method to schema builder