Add book on Backbone.js, sort Backbone books

Added: Building Single Page Web Apps with Backbone.js
Fix sorting order
dodaje pythona, c, c++, sql
Adding AJAX to the list. Edit some books positions to be consistent with: CONTRIBUTING.md
Merge pull request #687 from matysanchez/master

Adding AJAX to the list. Edit some books positions to be consistent with: CONTRIBUTING.md
Merge pull request #686 from agilob/patch-1

adding python, c, c++, sql to the list in Polish
Merge pull request #681 from JIghtuse/master

Add book on Backbone.js, sort Backbone books