First improvement for App's model #7

New fields :
- Date of publication
- Date of last Update

AND

Validation functions but the integration of these functions makes
troubles for adding apps ... TO FIX
Improvement on the server API #41

Changing some stuffs to work with angular implementation of the web
application
Improvement on App Controller #48

1. Changing name to specify what it concerns.
2. Implementing all the defined actions in server API
Views & contents

- Default image for app icon
- Home Page
- improve index page (containing the off canvas)
- Partials for : apps'list, C/R/U/D an app