FEATURE: Category Page SEO Friendly Links

Added SEO friendly link tags for Categories that are more than one page.

If a category has more than one page the following tags will be inserted into the head tags when appropriate:

<link rel="prev" href="/dvd-movies?pi=1" />

<link rel="next" href="/dvd-movies?pi=3" />

If the currently viewed page is the first page of the category there will only be a next and if the currently viewed page is the last page there will only be a prev.

All pages in between the first and last will have next and prev.

This makes paginated category pages work how this Google Blog describes:
http://googlewebmastercentral.blogspot.com/2013/09/pagination-with-relnext-and-relprev.html