Improve Keyword/Tagging System

[gothick]

Add links to all tags that link to a tags page, that displays all images with that tag, paginated. This will probably mean rewriting the way tags work; we don’t want them in an array any more; they’ll have to be split into their own table. There’s a nice-looking package here for that: https://github.com/Bee-Lab/BeelabTagBundle/blob/master/docs/index.md