Various internal refactor proposals

* BackbonedController refactor, now a singleton (it feels OK in this context)
* Added condition to show comment form only when they are open
* Adjusted date format to leverage filter and user options for formatting preferences
* Better support for i18n-ed dates
* Ability to use backboned2 as a child theme
* Made error documents more generic, added 403
* Notes on how to add i18n on Mustache templates
* Refactoring BackbonedController so it is called only once
* Adding body class to use WordPress internal