Add singleton to db class
Merge remote-tracking branch 'origin/master'

Conflicts:
	application/models/model_admin.php
	application/models/model_authorization.php
	application/models/model_images.php
	application/models/model_leftmenu.php
	application/models/model_main.php
	application/models/model_mainmenu.php
	application/models/model_message.php
	application/models/model_news.php
	application/models/model_products.php
	application/models/model_registration.php
	application/models/model_search.php
	application/models/model_user.php