Requests for comment/HTML templating library

Currently several MediaWiki extensions make use of JS or PHP HTML templating libraries. It would be ideal to standardize on one library and add it into MediaWiki core. This is similar to the situation that existed regarding CSS languages before LESS support was added to core and made the standard.

Justification

 * Better code readability, editability, and portability
 * Separate code from markup
 * Avoid jQuery spagetti
 * Avoid loading multiple JS libraries from different extensions

Existing implementations in MediaWiki extensions

 * PageTriage uses Underscore.js
 * MobileFrontend uses Hogan.js (Twitter's implementation of Mustache.js)
 * DonationInterface uses a custom template system (RapidHTML)
 * ArticleCreationHelp uses a custom template system

Templating library options
Hogan/Mustache has both a PHP and JS implementation.

Implementation
...