Multi tagging navigation

Multi tagging navigation has been completed. Let me know if there is something to improve. You can temporary see it working here: http://54.76.229.230

From the home page click on a tag first and then on another one. Notice the new URL (which concatenates tags with +), the tag links and the light blue message like "Filtering by tags: galaxy OR motif - Reset". Example: http://54.76.229.230/t/galaxy+motif/