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