[NFR] Support for self/parent/static scopes in static properties

This will allow to handle the situations like this:

```php
class A
{
    static $prop = 1;

    public static function get()
    {
            return static::$prop;
    }
}

class B extends A
{
    static $prop = 2;
}

echo B::get(), "\n";
```

This can be useful if a child class wants to override parent's static property.

Supported types:
  * self::$property;
  * parent::$property;
  * static::$property (late static binding).

Added functions:
  * phalcon_fetch_self_class(): fetches zend_class_entry* corresponding to self;
  * phalcon_fetch_parent_class(): fetches zend_class_entry* corresponding to parent;
  * phalcon_fetch_static_class(): fetches zend_class_entry* corresponding to static;
  * phalcon_read_static_property_ce(): same as phalcon_read_static_property() but uses zend_class_entry* instead of class_name;
  * phalcon_update_static_property_ce(): same as phalcon_update_static_property() but uses zend_class_entry* instead of class_name;
  * phalcon_read_class_property(): phalcon_fetch_XXX_class() and phalcon_read_static_property_ce() combined