Improve discoverability of "add new preset"

On the admin/content/types page we have a pattern that there is a tab to take the action of adding a new content type, but also a link at the bottom of the page. This change came out of the University of Minnesota usability studies where people didn't see the tabs, but did look at a lot at the middle of the page.

I think the imagecache presets page has a similar problem which could use a similar fix.

Before:

After:

Yay!