[#30058] Quotes are not escaped in popup-manager.js

This pull request adds new method htmlEntities to ImageManager class. This method is used to replace quotes and brackets in alt and title attributes of images, that are inserted with com_media>images modal. 
Link to tracker record: 
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30058