Added some Glyphicons here and there, renamed a partial

* Added a "gift" icon on "free book" labels
* Added a "download" icon on "download ebook" labels
* Renamed "book-display" partial to more explicit "book-short-display"
Bugfix: remove accents in downloaded ebooks files names

* Added "jbroadway/urlify" library
* Added a wrapper for its "downcode" method in our own StringUtils Service
* We now use this "removeAccents" Service method for downloaded ebooks files names