Reduce the need to copy the permitions from the database

The need to use the permission constants is removed.

The ability to use

```php
$rights = Rights::instance();
if ($user->can($rights->edit_users))
```
instead

```php
<?php
class Model_Permission extends ACL_Model_Permission {
	const EDIT_USERS = 1;
	const ADD_NEW_POST = 2;
}

$user->can(Model_Permission::EDIT_USERS);
```
is presented.

The rights are taken from Permissions::name field in the database. For example `add_new_post` right in the database is presented as `Add new post`, `edit_user` as `Edit user`.