[REST API] Users API

Fix for [WOBS-3019] follow topics form

Users API:
* [x] Register user
* [x] Log in user

**Action of login form must be: "/auth/login_check" in templates.**
* [x] Restore user password
* [x] Load confirmation email, restore password email text directly from templates

Others:
* [x] Setting placeholders through smarty. E.g. usage:

New usage:
```
{{ set_placeholder subject=sprintf("E-mail confirmation at %s", $site) }}

or simply:

{{ set_placeholder subject="Some test subject" }}
```
Old usage: 
```
{{ $view->placeholder('subject')->set(sprintf("E-mail confirmation at %s", $site)) }}
```

* [x] Replace Zend Auth on frontend by Symfony2 login
* [x] Fixed template caching in response
* [x] New comments notification service rewrite
* [x] Rewrite EmailService