Allow members to like posts by default and add setting

closes flarum/core#344

extensions/likes/migrations/2015_09_04_000000_add_default_like_permissions.php

@@ -0,0 +1,39 @@
+<?php
+
+use Illuminate\Database\Schema\Blueprint;
+use Flarum\Migrations\Migration;
+use Flarum\Core\Groups\Group;
+use Flarum\Core\Groups\Permission;
+
+class AddDefaultLikePermissions extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        $permission = Permission::firstOrNew($this->getPermissionAttributes());
+
+        $permission->save();
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Permission::where($this->getPermissionAttributes())->delete();
+    }
+
+    protected function getPermissionAttributes()
+    {
+        return [
+            'group_id' => Group::MEMBER_ID,
+            'permission' => 'discussion.likePosts'
+        ];
+    }
+}