Created admin module with Gii
Configured admin module and added controllers with Gii

- configured admin module in config/web.php
- added controllers for Post and Comment in admin module using Gii
Added main layout for admin section
Updated post grid in admin module
Updated post _form in admin module
Added status constants to Post model in admin module
Updated comment view files in admin module and enabled approving comments

- updated index and view files in comment views
- deleted unused views
- added methods for approving comments
Removed create comment button
Changed button size in admin views
Changed default route in admin module
Added Login functionality to admin module

- moved User and LoginForm models to admin module
- added config file for admin  module
- added login and logout methods to DefaultController in admin module
- added access filters to controllers
Fixed login redirection after logout