Modified method CClientScript::renderCoreScripts() for interpreting arrays in packages.

Small changes in CClientScript::renderCoreScripts() implement a feature to register a js file in the specified position of HTML page.

Example:
```php
packages =>[
 'main' => [
  'js' => [
   'js/one.js',
   ['js/two.js, CClientScript::POS_END'],
   'js/three.js'
  ]
 ]
]
```