[Please Review before merge] Fixed static in signature error

The static key-word cannot be used in method-signatures and static context, which is evaluated at compile time (assignment to static variable in function)
Possible fixes:
```php
function f(){
    static $var;
    if($var === null){
        $var = array();
    }
}
```
However, that would render static senseless. I opted for replacement. As constant overriding should not be common.
`
D:\dev\www\vhosts\yii2\framework>yiic app/create ./../
exception 'yii\base\ErrorException' with message '"static::" is not allowed in c
ompile-time constants' in D:\dev\www\vhosts\yii2\framework\helpers\base\Console.
php:459
Stack trace:
#0 D:\dev\www\vhosts\yii2\framework\base\Application.php(120): yii\base\Applicat
ion->handleFatalError()
#1 [internal function]: yii\base\Application->end(0, false)
#2 {main}
`