Plug application task

This is a attempt to make the application use the [task manager](https://github.com/xwiki-contrib/application-task) as a task tool into the project application.

In order to do that, the pom has been updated to follow some standard of XWiki development (mainly using the xar plugin) which explains the big diff (the whole xml files has been reordered).

French translations of the project application has also been added.