Update Migration + Fix SQLSTATE

1) Added foreign keys for a better database consistency.

2) Fixed - If you have a user without any permission and you try to do a  "Redoubt::getPermissions($user)" you will get an SQLSTATE.

"SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 1 (SQL: select * from `group_object_permission` where `group_id` in ()) (Bindings: array ( ))"


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<h4>Improvements</h4>
- It would be nice to add some Unit Testing.


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You did a great job ;) Really useful repo !