Added manage articles in panel admin + fix few bugs

Added the articles management in the admin panel, added the interface in the panel admin, fix  archive bug in blog cell, added routes for the panel admin
Fixed travis build
Fixed is_display for display articles
fix indentation
Added management categories + fix few bugs

Added management categories + fixed a bug when a category doesn't have any article + updated the schema of the database
Fixed bug when creating an article with the same title as another article
Added dashboard
Added Browsers in dashboard
Use isAuthorized() instead of beforeFilter() to check if an user can access to the panel admin
Fixed PHPCS errors
Added Continents in dashboard
Updated Readme
Merge pull request #1 from Xety/panel-admin

Add Panel Admin