Move Group to its own namespace

We’ll need to add commands etc. for group management in the future

src/Core/Users/Group.php

@@ -1,36 +0,0 @@
-<?php namespace Flarum\Core\Users;
-
-use Flarum\Core\Model;
-
-class Group extends Model
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $table = 'groups';
-
-    /**
-     * The ID of the administrator group.
-     */
-    const ADMINISTRATOR_ID = 1;
-
-    /**
-     * The ID of the guest group.
-     */
-    const GUEST_ID = 2;
-
-    /**
-     * The ID of the member group.
-     */
-    const MEMBER_ID = 3;
-
-    /**
-     * Define the relationship with the group's users.
-     *
-     * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany
-     */
-    public function users()
-    {
-        return $this->belongsToMany('Flarum\Core\Users\User', 'users_groups');
-    }
-}

src/Core/Users/Guest.php

@@ -1,5 +1,7 @@
 <?php namespace Flarum\Core\Users;
 
+use Flarum\Core\Groups\Group;
+
 class Guest extends User
 {
     /**

src/Core/Users/User.php

@@ -1,5 +1,6 @@
 <?php namespace Flarum\Core\Users;
 
+use Flarum\Core\Groups\Group;
 use Flarum\Core\Model;
 use Flarum\Core\Notifications\Notification;
 use Illuminate\Contracts\Hashing\Hasher;
@@ -487,7 +488,7 @@ class User extends Model
      */
     public function groups()
     {
-        return $this->belongsToMany('Flarum\Core\Users\Group', 'users_groups');
+        return $this->belongsToMany('Flarum\Core\Groups\Group', 'users_groups');
     }
 
     /**