InMemoryRoleProvider can reuse role objects

[Wilt]

In the current setup the child role in a HierarchicalRole is another Role instance with the same name. This is because of how the InMemoryRoleProvider is creating the roles. For example the $memberRole in the InMemoryRoleProviderTest is not the same object as the first child role of the $adminRole.

It would be cool to change the setup so that these tests are successful. I also think it will save some memory because in this case the roles are instantiated only once.

assertTrue($adminRole->getChildren()['member'] === $memberRole);
assertTrue($memberRole->getChildren()['guest'] === $guestRole);

[danizord]

Looks good for me, can you provide a PR @Wilt?

[Wilt]

Here a PR

[danizord]

Fixed by #325