Migration fixes

This fixes the migration command and generator to use the settings in config.php.
Changes:
1.) Fixed MigrationCommand.php
and migration.blade.php to use configured
settings.
2.) Changed assigned_roles to user_role in
config.php, EntrustRole.php, HasRole.php.
3.) Fixed variable name in Entrust.php.
4.) Applied detab.

Issue:
 IMHO, we should delete the lines I have commented out in MigrationCommand.php. I have them commented out b/c I'm not sure how to handle the migration command options.

In the current master branch, `entrust:migration` has an option to change the name of the roles table. This raises some issues. Firstly, why single out the roles table for special treatment? Why not include options to change the names of the other tables? Secondly, these options force the user to update config.php so that the values match the option values they passed to `entrust:migration` (this is important since config.php is accessed throughout the package via the Config facade). If this is the case, they may as well just modify config.php in the first place and not pass options to `entrust:migration`.