Rename `tagregator_item_class` to be more consistent with others filters.


git-svn-id: https://plugins.svn.wordpress.org/tagregator/trunk@1005442 b8457f37-d9ea-0310-8a92-e5e31aec5664
Pass raw `$classes` array to `tggr_item_css_classes` callbacks.

It's easier and safer to manipulate the raw array than a derived string, especially if multiple plugins are filtering it.


git-svn-id: https://plugins.svn.wordpress.org/tagregator/trunk@1005444 b8457f37-d9ea-0310-8a92-e5e31aec5664