Fix for issue 347 > Can't choose which share buttons to display

http://forkcms.lighthouseapp.com/projects/61890-fork-cms/tickets/347-share-buttons-cant-choose-which-buttons-to-display

jquery.extend with true (deep extend) doesn't overwrite an array but merges it. I've split up the defaults into defaults and settings so that they both can be used by jquery.extend. But only the settings will do a deep extend.

More info: http://api.jquery.com/jQuery.extend/ & http://bugs.jquery.com/ticket/9477