Twig: add access to Var store

Documentation/Report.rst

@@ -250,6 +250,7 @@ QFQ also provides access to the following stores via the template context.
   * typo3
   * user
   * system
+  * var
 
 All stores are accessed using their lower case name as attribute of the
 context variable `store`. The active Typo3 front-end user is therefore available as::

extension/Classes/Core/Report/Report.php

@@ -802,6 +802,7 @@ class Report {
                 'typo3' => $this->store->getStore(STORE_TYPO3),
                 'user' => $this->store->getStore(STORE_USER),
                 'system' => $this->store->getStore(STORE_SYSTEM),
+                'var' => $this->store->getStore(STORE_VAR),
             )
         ));
         return $contentTwig;