Removing MooTools from validation.js and adding improvement to cache DOM queries

I have been working on removing MooTools dependencies in Joomla CMS for the GSoC2013 project. This PR includes the removal of MooTools dependencies from validation.js. I have also included DOM query caching in certain places to reduce DOM access for each validation.

Feature Tracker Item:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31575&start=500
@mbabker Can you confirm that this is still unresolved? Looking at https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/document/html/renderer/head.php#L220-L253 and https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/language/text.php#L17 I cannot figure out the current situation. Thanks