rename "add page" button to "sitemap"

Maybe it's just me, but to me "sitemap" is the main functionality and not "add page". I know that add page gets a bit less visible due to that change, but so is sitemap.. "Add Page / Sitemap" is a bit too long, isn't it?

![image](https://cloud.githubusercontent.com/assets/129864/5068341/84f8216a-6e4d-11e4-8e26-68340ee84ac3.png)