[3.9] Add grunt task utilities

- [x] Add a task to build assets
- [x] Change assets path to new assets target directory
- [x] Add task to run JS tests and remove test/js/run.sh script ...
- [x] Update travis build
- [x] Check if dependencies in www/include/js/lib/* can be added to bower (tinymce, jqmobile etc ... )
- [x] Move www/skins/build to www/assets/builds 
- [x] Update dependencies:bower developer task
- [x] Remove assets:compile-less developer task
- [x] Remove asset:build-javascript developer task 
- [x] Remove unused assets in www/include/js/lib see #567 
- [x] Tests plugins mechanism
- [ ] ~~Add production mode for building assets without dev dependencie~~  see yatskevich/grunt-bower-task#59
- [ ] ~~Add a package task~~