[Twig] Support array like variables in type completion

[Haehnchen]

Currently supporting form/class/formfield in twig variable completion. also adding array key completion provider. at least needed for drupal8 templates, but also reusable in symfony2 controller context

• controller var collector
• variable provider + refactoring of main twig vars handling

array(
  'foo' => array(
    'foo1' => new \Class()
  )
)

see ArrayReturnPsiRecursiveVisitor:
https://github.com/Haehnchen/idea-php-laravel-plugin/blob/master/src/de/espend/idea/laravel/util/ArrayReturnPsiRecursiveVisitor.java