add post_model and post function
Merge branch 'master' of github.com:chenjinhui314/yangchenhouse

Conflicts:
	application/controllers/admin.php
	application/models/user_model.php
	application/views/admin/admin.php
	application/views/admin/create_node.php
	application/views/admin/login_view.php
	application/views/header.php