Grunt integration and french translation

Result of latesest meetup (plus some cleanups :P)

Grunt integration in play to allow angular tests to run
- project structure modified (all front-end assets are in the ui folder and grunt will minimise/coffeeize/lessize/copy them in /public where play will serve them
- main.coffee separated in different files (directives, controllers, services) to increase Maintainability :)
- JavascriptBuild.scala deactivate Play's control over javascript to let Grunt do his job
- Added command NPM to install dependencies needed for grunt
- Added command Grunt "name_of_grunt_task" to run a specific grunt task (or just grunt to run the default task)
- play run will call the default grunt task

French translation
- angular_locale_fr added
- messages.fr added