Fixed error when Meteor Slides is not installed

Issue resolved by adding error handling:
viewing wp-admin/customize.php with the Meteor Slides plugin not
installed throws a PHP notice: "Notice: Trying to get property of
non-object in [...]/uu-2014/inc/customizer.php on line 46"
Fixed floating sidebar width

Fixed following issue by making the width of the floating sidebar
responsive to the width of the widgets:
any widgets added to floating sidebar that aren't just social sharing
icons result in partially-visible, broken-looking content in that space