Clear cache of pages is now handle by PageManager

Clear cache logic is now in Page class, we didn't care wich attributes we have to alter in the page to clear the cache
 #122: Add website clear cache button
#126 : Handle custom page with specific controller

Create an abstract controller which will be the base for every custom controller.
Routing will be done with standard Symfony routing
fix modifications typo inside translation files
#126 : Abstract class should be abstract
remove clearCache logic form clearCacheAction

Logic has been moved to PageManager inside clearCacheFromWebsite
add useful comment to explain how cache are cleared in the page
#126 : add a renderResponse method to ease code
if something went wrong during cache clear we only show to the user the default flash message
move inline comment to phpdoc comment
Merge pull request #132 from BenoitLeveque/clear-website-cache

Add a clear website cache on website admin page
Merge pull request #133 from prestaconcept/Issue126_handle_custom_controller_action

#126 : Handle custom page with specific controller