related measures listed on tag edit page, superuser can edit category,
check for existing tags before save.

Add: related measures and count displayed on tag edit page
Add: only superuser can edit and save category
Add: case insensitive check nefore saving tags on tag edit page
Add: notification text when saving duplicate tag
Fix: now hiding tag edit button for non admins
added tooltip on review page when not an admin, fixed cancel button on
new measure page, centered approve button.
using common method to determine if tag exists in backbone.
refactored code for finding and creating tags in backbone models.